Mhofanuraimc Nural Olling Mating:' I'n- Th Aleopard Frog, 1Ana

THE SEXU-AL B:EHAVIOR

MHOFANURAIMC NURAL OLLING MATING:' I'N- TH ALEOPARD FROG, 1ANA. PIPIENS

LESTER -R. ARONSON AND G. KINGSLEY NOBLE

BULLETIN.- OF THE: AMERIC-AN MUSEUM'.OF NATURAL HISTORY- VOLUME 86 : ARTICLE 3 NE-NVNKYORK. 1945

THE SEXUAL BEHAVIOR OF ANURA

2. NEURAL MECHANISMS CONTROLLING MATING IN THE MALE LEOPARD FROG, RANA PIPIENS LESTER R. ARONSON Assistant Curator, Department ofAnimad Behavior G. KINGSLEY NOBLE Late Curator, Departments of Herpetology and Experimental Biology

A DISSERTATION SUBMITTED BY THE FIRST AUTHOR TO THE FACULTY OF THE GRADUATE SCHOOL OF ARTS AND SCIENCE OF NEW YORK UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY

VOLUME 86 : ARTICLE 3 NEW YORK -* 1945 BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY Volume 86, article 3, pages 83-140, text figures 1-27, tables 1-5 Accepted for publication December 4, 1944 Issued November 19, 1945 CONTENTS

INTRODUCTION ...... 89

LITERATURE ...... 91

MATERIALS AND METHODS ...... 95

RISUME OF NORMAL MATING PATTERN ...... 97

MAJOR NUCLEAR MASSES OF THE FROG BRAIN...... 98 EXPERIMENTAL PROCEDURES AND RESULTS ...... 105 Swimming Response of the Male to the Female ...... 105 Emission of the Warning Croak ...... 108 Sex Call ...... 108 Clasp Reflex...... 109 Spawning Behavior...... 110 Release after Oviposition ...... 113 DESCRIPTION OF OPERATED BRAINS AND SUMMARY OF BEHAVIORAL DATA 117

DISCUSSION ...... 129

SUMMARY AND CONCLUSIONS ...... 135

LITERATURE CITED ...... 136

ABBREVIATIONS FOR ALL FIGURES ...... 139

INTRODUCTION ALTHOUGH SOME of the very early concepts of ine some of these concepts from the behav- the neural mechanisms controlling sexual be- ioral point of view. havior were developed from experimentation While the anuran brain exhibits a consid- on Anura, almost all the recent investigators erable amount of specialization as compared in this field have concentrated on mammals. with that of the urodele, the technical advan- The rapid progress made in the last two dec- tages gained by using the frog, particularly ades in this aspect of mammalian research Rana pipiens, were such as to make this spe- has not been paralleled in the lower verte- cies particularly desirable, at least for an in- brates. In Anura, few advances have been troductory investigation. made in this subject since the close of the In developing the project we attempted to last century. utilize, wherever possible, recent methods and Some of the earlier investigators probably techniques. Foremost among these is the pi- chose the frog because lesser technical prob- tuitary injection method developed by Rugh lems were involved in brain experiments on (1935) which made available to us an abun- this animal, but a more important reason for dant supply of sexually active leopard frogs investigating the neural mechanisms of Am- for eight consecutive months in the year. phibia is now apparent. It is generally ac- Other techniques such as the use of suction cepted that the amphibian brain closely and electrocautery for producing brain le- resembles the generalized prototype from sions, and the sectioning and reconstruction which the higher vertebrate brains developed of the operated brain enabled us to localize (Kuhlenbeck, 1921; Herrick, 1933a). Many more precisely than heretofore the function- of the ancient pathways of the amphibian ally important areas in the frog brain. Fi- brain are still recognized in the mammalian nally, the results of hours spent learning and and human brains (Papez, 1929; Ariens Kap- quantifying the normal mating patterns pers, Huber, and Crosby, 1936). Relatively (Noble and Aronson, 1942) proved to be an speaking, the frog brain is organized along invaluable aid in interpreting the effect of very elementary lines, and this is reflected in brain injury upon sexual behavior. the simple and extremely stereotyped mating The present study was designed to survey patterns which these animals exhibit. Hence in a general way the effects of brain depriva- information concerning the mechanisms of tions on various phases of the mating pattern. the innate behavior patterns of these primi- Intensive investigation of any particular tive vertebrates should be of considerable phase was left for future investigation now value in interpreting mammalian and human contemplated. brain function (Beach, 1942a) and in formu- lating general theories of the evolutionary changes in the nervous control of this very ACKNOWLEDGMENTS important aspect of behavior. This study was initiated under the guid- For many years Dr. C. J. Herrick has been ance of Dr. G. Kingsley Noble, late Curator engaged in an exhaustive study of the mor- of the Departments of Herpetology and Ex- phology of the amphibian brain, and during perimental Biology of the American Museum the course of this work he has formulated a of Natural History and Visiting Professor of number of hypotheses concerning the func- Biology of the Graduate School of New York tion of the structural elements which he de- University. Dr. Noble's inexhaustible en- scribed in such detail. However, as Herrick ergy, unending enthusiasm, and inspiration (1933a) himself expresses it, "These are in- are gratefully remembered. Sincere thanks ferences drawn from the anatomical arrange- are due to Dr. Frank A. Beach for many val- ments, and for most of them there is as yet uable suggestions made during the final little direct experimental proof." The present course of this research, and also for his very experiments were intended, in part, to exam- helpful criticism of the manuscript. Thanks 89 90 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 are also due Dr. T.C. Schneirla for a critical fine histological preparations and to Miss reading of the manuscript. The generous as- Janet Roemhild for the illustrations.-L.R.A. sistance of Miss Arlene Douglis and Mrs. M. The experiments herein reported were sup- Madof in making some of the observations is ported by a grant from the Committee for acknowledged. Thanks are due to Miss Pris- Research in Problems of Sex, National Re- cilla Rasquin for the large number of very search Council. LITERATURE ROBERT BOYLE (1663), renowned physicist males which had just been separated from fe- and natural philosopher, was among the ear- males, he observed that one of the decere- liest experimentalists to investigate the be- brate animals reclasped a female. He inter- havior of frogs following the extirpation or preted this to be the result of the female's destruction of the brain. Boyle's experiments, accidentally swimming underneath the male and the studies of a number of investigators and stimulating the male's clasp reflex, that during the following century (reviewed by is, a simple local reaction rather than a gen- Eckhard, 1883), demonstrated the impor- eral response of the decerebrate male towards tance of the brain of the frog to the mainte- the female. nance of various vital functions such as heart Goltz (1869) confirmed Spallanzani's find- beat, respiration, and locomotion. More than ings relative to the tenacity of the male's a century later the great naturalist Spallan- clasp. He observed that the clasp reflex could zani (1786) demonstrated that during the be initiated by stimulation of the ventral breeding season clasping male frogs and toads pectoral skin and that frogs deprived of this would suffer excessive mutilation of their skin area no longer clasped. Moreover, a male bodies and hind limbs without releasing the could be induced to clasp the experimenter's females. When forcibly separated from the finger when it was rubbed against the pecto- females, these mutilated males soon re- ral skin. However, according to Goltz, a male clasped. Spallanzani decapitated clasping would soon release the finger, whereas when males, and found that they still remained in the pectoral region was stimulated by the amplexus for several hours, and separated back of a female, a lengthy clasp usually en- only when near death. On at least two sepa- sued. Males deprived of the cerebral hemi- rate occasions oviposition occurred while the spheres distinguished between the experi- decapitated frogs were coupling with normal menter's finger and a female as efficiently as females. These headless males fertilized the an intact male; but following ablation of the eggs, and viable tadpoles were recovered. entire brain, the animal attempted to em- Flourens (1824) was the first to report the brace and continued to clasp without discrim- loss of all spontaneous movement resulting ination, any object which touched his pecto- from forebrain extirpation, observing also that ral skin. Goltz concluded that a tonic em- the removal of only one cerebral hemisphere brace of the finger is not obtained in the caused no apparent behavioral changes. At intact animal because the brain transmits in- about the same time Desmoulins (1825), who hibitory impulses to the clasp reflex center was also studying the physiology of the anu- located in the spinal cord at the level of the ran brain, came to the opposite conclusion, brachial plexus, and at the same time the namely, that the. decerebrate frog still ex- brain sends excitatory impulses to many hibits spontaneous activity. His conclusion other centers in the spinal cord. was reached after observing the swimming Fromn other experiments investigating the activity of forebrainless animals in deep wa- functions of the forebrain Goltz (1869) ter. Here are found the beginnings of a con- stated that after various types of extirpa- troversy which has continued to the present tion, frogs lose "voluntary or spontaneous day. Desmoulins also showed that the decere- locomotion." Such frogs will not snap at in- brate frogs were not blind, for they could be sects, and during the breeding season decere- stimulated to jump accurately through a slot brate males will not pursue females. In in a board held obliquely in front of them. agreement with Desmoulins (1825) Goltz re- Most of the early investigators (Patton, ported that these forebrainless animals were 1846; Vulpian, 1866; Goltz, 1869; Onimus, not totally blind, since they avoided obsta- 1870; Steiner, 1885; Stroud, 1899) agreed cles when prodded to leap. Likewise, the de- with the viewpoint of Flourens. It is of inter- cerebrate males -were still sexually active est to note that after Vulpian had extirpated since they clasped firmly when placed on the the forebrains of a group of sexually active backs of females. 91 92 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 In Goltz's investigation of the croaking re- and Goltz (1869) to the effect that painful flex he observed that stimulation of the skin peripheral stimuli applied to a clasping male of the back at a point just caudal to the ax- eventually resulted in relaxation of the clasp. illae readily elicited the croak. The ob- Brain transection at the caudal end of the server's fingers or a similar smooth surface cerebral hemispheres did not affect relaxa- touching the skin proved to be an adequate tion of the clasp according to Tarchanoff. stimulus. This reflex was produced more uni- When the transections were made at the cau- formly in decerebrate frogs than in normals, dal level of the optic lobes, or just caudal to since the former never croaked unless stimu- the cerebellum, or at the caudal end of the lated in the above manner, whereas unoper- medulla oblongata, clasping males rarely re- ated males sometimes croaked without any leased even after the most intense and last- apparent stimulus. It was also demonstrated ing peripheral stimulation. From these ob- that transection through the optic lobes abol- servations it was concluded that impulses ished the croak. resulting from the painful peripheral stimula- Finally, Goltz reported that males which tion reach the dorsal thalamus and tectum. had been castrated during the breeding sea- From this point they are relayed to the spi- son continued to approach and clasp females. nal clasp center in the form of inhibitory im- Bechterew (1884) and Steiner (1885) ob- pulses. To verify this hypothesis, Tarchanoff served that removal of the midbrain roof did exposed the brain of a clasping male and not interfere with the croak reflex. When the punctured various areas with a sharp needle. base of the optic lobes was invaded, the oper- Punctures of the cerebral hemispheres and ates invariably croaked loudly at the mo- medulla oblongata did not modify amplex- ment the injury was inflicted, after which us, but a single, properly placed puncture of they could never again be stimulated to vo- the dorsal thalamus or optic lobes caused im- calize. mediate relaxation of the clasp. Steiner (1885) demonstrated that removal Using approximately the same methods, of the pallial part of the forebrain did not in- but working with toads, Albertoni (1887) ar- terfere with the so-called spontaneous behav- rived independently at essentially the same ior. He localized the mechanism for sponta- conclusion, namely, that the optic lobes are neity in the subpallium. inhibitory centers which play upon the pri- Tarchanoff (1887) removed the heart, mary clasp center in the anterior end of the lungs, various parts of the liver, the intes- spinal cord. tine, stomach, kidneys, and testes in male In all the investigations up to 1887, the frogs without producing any immediate frogs were tested shortly after operation. In slackening of the clasp; release of the female the experiments of Schrader (1887) ample occurred only when the operated male neared time was allowed for the wounds to heal. The death. When the seminal vesicles (caudal ex- experimental frogs were induced to hibernate panded portion of the Wolffian duct) were over the winter and were first tested the fol- opened and drained, or surgically removed, lowing spring. Contrary to the findings of the the male frogs immediately lost all sexual ac- majority of previous investigators, Schrader tivity, and released. Tarchanoff refilled the observed that decerebrate frogs exhibited vesicles with water or milk and noted an im- spontaneous activity. Thus Schrader sup- mediate resumption of sexual activity. These ported the earlier contentions of Desmoulins. observations led to the conclusion that affer- These decerebrate frogs snapped at food ent stimuli responsible for the sexual clasp quite readily, and sought females with the arose from the seminal vesicles which were same ardor as the intact animals. However, distended by the accumulation of semen. As when the optic thalamus was extirpated in a final proof, Tarchanoff ligated all periph- addition to the forebrain, a considerable re- eral nerves leading to the seminal vesicles and duction in spontaneous activity occurred. obtained an immediate cessation in sexual To harmonize his observations with the op- activity. posing results of previous investigators, In a second investigation Tarchanoff (1887) Schrader postulated that these workers must utilized the observations of Spallanzani (1786) have inadvertently damaged the diencepha- 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 93 Ion while removing the forebrain, and that all the frog's blood and substituting saline the loss of spontaneity which they observed solution. No reduction of the clasp was noted. was in reality due to the thalamic injury. Hence it was concluded that the clasp did not This conclusion was accepted by Fritz depend upon hormones carried in the blood Edinger (1913) in his review of the physi- stream. Busquet (1910a) observed that the ology of the central nervous system of the clasp can be elicited any time of the year fol- frog. lowing cerebellar injury, and that the clasp Schrader contradicted Goltz's interpreta- mechanism is not present in females and im- tion of the neural mechanism mediating the mature males. croak, holding that destruction of the optic Burnett (1912) remarked that the decere- lobes did not abolish this behavior. The me- brate frogs which he observed exhibited a re- dulla oblongata was designated by Schrader duction in spontaneous activity. On the other as the "center" for the croak reflex. Schrader hand they caught flies more readily than nor- placed the inhibitory or modifying "center" mals, since the intact animals generally spent of the spinal clasp reflex in the anterior part their time in attempts to escape from captiv- of the medulla, rather than in the midbrain ity. Burnett concluded that "the reflex ex- where the earlier authors had concluded it citability of the decerebrate frog is heightened was situated. owing to the loss of inhibitory influences from Schrader's contentions were supported by the higher centers." Loeser (1905) who noted that decerebrate Baglioni (1913) reviewed some of the ear- frogs readily caught flies. A week after Loeser lier literature and reported in addition some transected the brains of male frogs just ros- further experiments on the clasp reflex (1911). tral to the medulla oblongata the croak reflex When he stimulated the optic lobes of a returned. clasping male with a faradic current, the Steinach (1910) observed that the inhibi- clasp became even stronger. When the optic tory center for the clasp reflex was located in lobes were narcotized by placing on them a the optic lobes, but he found additional in- cotton pledget soaked in "stovaine," clasp- hibitory centers in the medulla oblongata, ing soon ceased. He therefore concluded that since removal of the latter caused a clasp the optic lobes were an irritative rather than even stronger than normal. Steinach be- inhibitory center for the spinal clasp reflex. lieved that the peripheral impulses for the Baglioni hypothesized that during the breed- clasp reflex arose mainly from the stimula- ing season the testes produced internal secretion of the thumb pads, and only secondarily tions which, by stimulating the optic lobes from the pectoral skin as Goltz (1869) had to produce excitatory stimuli, acted upon the reported. spinal clasp center to cause the heightened Whereas Tarchanoff (1887) claimed that clasp. He also drew a distinction between the the internal stimuli for sexual activity arose sexual clasp and the clasp produced by mid- through distension of the seminal vesicles and brain or bulbar injury, which he believed to was a purely nervous phenomenon, Steinach possess a locomotor function. (1894, 1910) found that impulses arose pri- Blankenagel (1931) studied in somewhat marily from the testes and were hormonal. greater detail the effects of forebrain extirpa- This conclusion was based upon the observation, although not particularly in relation to tion that castration reduced the clasp, and sexual activities. He allowed the wounds to the injection of testicular substance increased heal thoroughly before making his observa- this response. Steinach (1910) even thought tions, and was able to refute Schrader's (1887) that implanted brain tissue, particularly mid- and Loeser's (1905) claims that decerebrate brain of the male, would strengthen the frogs do not lose their "spontaneity" of loco- clasp. motion. Blankenagel localized in the subpal- The experiments of Busquet (1910) located lium the region necessary for spontaneous the inhibitory center for the clasp reflex in the locomotion. He also found that decerebrate cerebellum, and this investigator attempted frogs did not seek food despite starvation for to demonstrate the independence of the clasp as long as a whole year. According to Blanke- reflex from internal secretions by drawing off nagel the region necessary for active food get- 94 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 ting is located in the posterior end of the sub- oviposition appear to be entirely normal af- pallium. ter total forebrain extirpation. Fertile eggs Confirming an earlier observation by Goltz may be recovered after an oviposition of a (1869), Blankenagel (1931) observed that the normal female when clasped by a forebrain- croak can be elicited more regularly in the de- less male. cerebrate frog than in the intact animal. The To summarize the results of the above in- spontaneously occurring croak heard in the vestigations, the following major generaliza- ponds during the summer (which is undoubt- tions appear to be warranted despite numer- edly the sex call as described in- our account ous contradictions: of mating behavior) was never emitted by 1. There appears to be a reduction in the decerebrate male. "spontaneous activity" after forebrain dep- Diebschlag (1934) also refuted Schrader's rivation, but this change is not evident if the (1887) claims relative to the loss of "spon- base of the forebrain remains intact. Non-re- taneity" after cerebral extirpation. He at- sponsiveness to food and to the female appear tempted to explain the discrepancy between to be manifestations of this reduction in his own findings and those of Schrader, first "spontaneity." by noting as did Steiner (1885) and Blanke- 2. A neural mechanism essential to the oc- nagel (1931) that if the base of the cerebrum currence of the clasp (primary clasp center) is left intact, there will be no noticeable de- is located at the rostral end of the spinal cord. crease in spontaneous activity, and second by 3. The activity of the primary clasp center suggesting that Schrader probably did not is modified by secondary clasp centers lo- remove all the forebrain in the operated frogs cated possibly in the thalamus, midbrain, designated as decerebrates. Whereas Blanke- cerebellum, and/or medulla oblongata. nagel recognized in the base of the forebrain 4. Following extensive midbrain lesions, one mechanism for spontaneous activity and frogs do not croak. The mechanism for vocal- another for feeding, Diebschlag considered ization appears to be located in the base of the irresponsiveness of the decerebrate frog the tectum. towards food simply as a manifestation of the 5. Forebrain deprivation does not modify loss of "spontaneity." the spawning movements of the male during Turning to sexual activities, Diebschlag oviposition. reported that the ability to recognize the fe- The relationship of the nervous system and male as a result of a specific tactile stimulus sexual behavior in other vertebrates will not is absent in the decerebrate male. be considered here since a number of reviews Recent preliminary findings by Noble and of this literature have been published in re- Kelman (unpublished) indicate that the cent years (Stone, 1939; Bard, 1940; Young, spawning movements of the male frog during 1941; Beach, 1942; 1942a; 1944). MATERIALS AND METHODS

THE READER IS REFERRED to an earlier paper During operations in which bleeding was by Noble and Aronson (1942) for the methods marked, low pressure suction was used to of maintaining the intact frogs and for ob- keep the field clear while the bone was being taining estrous (ovulated) females. Operated removed as rapidly as possible. With the suc- males were isolated in eight-liter aquaria con- tion still clearing the field of blood, the de- taining one-half centimeter of water which sired lesion was made, after which the bleed- was changed daily. A flat stone at one end of ing was controlled by cotton pledgets, adren- each aquarium provided a dry area. alin, or bone wax as previously described. Lesions in the preoptic area, hypothala- OPERATIVE PROCEDURES mus, and tegmentum were accomplished by Four operative techniques were used to re- means of a ventral approach. With the frog move various regions of the brain, namely, securely tied on its back, and its mouth low pressure suction (using an ordinary fau- clamped widely open, a median longitudinal cet aspirator), high pressure suction (approx- incision was made in the mucous membrane imately 10 gr./sq. cm.), electrocautery, and lining the roof of the oral cavity. The optic combinations of the above. Two types of op- chiasma which was visible through the semi- erations were performed, extirpations and transparent os parabasalis was used as a transections. With one exception, which will landmark. The desired region of the para- benoted later, suction was used forthe transec- basal bone was chipped away with a fine pair tions, and to secure complete separation a of scissors, and the underlying chondrocra- segment at least 1 to 2 mm. in thickness was nium was removed with the same instrument. removed anterior to the level to be studied. In removing the preoptic area attempts were Bleeding was minimized in many cases by made (which were usually, but not always, applying a 1:100 solution of adrenalin chlo- successful) to avoid severing the laterally ride. Where large amounts of brain tissue had overlying anterior rami of the cerebral carotid been removed, soft bone wax was used to fill arteries (Gaupp, 1899). The pituitary injec- the cranial cavity. tions mentioned above were used to increase In the first group of experiments, the males the sexual activity of the operated frogs, were anaesthetized with a 3 per cent solution since it has been shown that without such of urethane. Immediately following the oper- treatment only one-third of the males in cap- ation they were injected with one or two ante- tivity are sufficiently stimulated to clasp es- rior pituitary glands from females, and tests trous females (Noble and Aronson, 1942). were started on the following day. Through- out the period of observation each operate OBSERVATIONS OF BEHAVIOR was injected daily with one or two pitui- As already stated, the observations were taries. In the subsequent experiments it was begun within one hour to one day after the found more expedient to start the pituitary operation. In most instances the tests were treatment the day preceding the operation. completed within one week, after which the The surgery was then performed without an- operates were killed by decapitation. Many aesthesia, and tests were begun one to two of the operates with very extensive lesions hours after the operation. died before all the desired tests had been com- The dorsal approach was used for the ma- pleted. The procedures used, together with jority of the operations. The skin was incised other details of method, are given in the de- longitudinally along the midline and tied lat- scriptions of the various experiments which erally with hooks. Next, the frontoparietal follow. bone was carefully chipped away under a dis- section microscope with a fine pair of scis- DETERMINATION OF THE EXTENT sors. Special care was taken to avoid tearing OF THE BRAIN INJURY the laterally situated orbitonasal arteries. The heads were fixed in 10 per cent for- When it was necessary to expose the dien- malin, after which the brains were removed cephalon, some bleeding usually occurred. and the blood clots and meninges carefully 95 96 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 dissected away. Both the dorsal and ventral drawn indicating the nuclear masses and aspects of the brains were photographed, and other outstanding landmarks. These sketches in addition a sketch and written description were reduced, assembled, duplicated, and em- of the gross aspects of the lesion were made. ployed as standard charts upon which the le- The brains were embedded in paraffin, sec- sion in each operated brain (as determined by tioned transversely at 15 ,u and stained with microscopic examination) was plotted. gallocyanin (Einarson, 1932). The description of the topography of the For control and general reference, an aver- normal Rana pipiens brain, the lesion in each age size Rana pipiens brain was similarly operated brain, and the drawings of the nor- treated. Every seventh or eighth section from mal and experimental brains were made in the olfactory bulbs to the medulla oblongata part from these sketches. was projected, and outline diagrams were RtSUM]e OF THE NORMAL MATING PATTERN

IN THE FOLLOWING BRIEF OUTLINE of the sex- against the back of the female. The male's ual behavior of Rana pipiens, emphasis is back is slightly arched convexly, and his placed on those phases of the male's behav- lower extremities remain tightly flexed. The ior which were tested after brain depriva- male remains in this position until the spawn- tions. For further details, the reader is re- ing begins. Within a few minutes to several ferred to the description of the normal mating hours after the onset of amplexus, the female pattern by Noble and Aronson (1942). exhibits peculiar backward movements which In the spring when the frogs are in the we have termed "backward shuffling." Al- breeding ponds, the croak most frequently ternate periods of backward shuffling, rest, heard is known as the sex call. It can be rep- and swimming activity occur. As the time resented phonetically as an "ir-a-a-a---a-a- for the spawning approaches, the female as- h," starting softly, and gradually growing sumes the oviposition posture. Her thighs ex- louder as the vocal sacs become inflated. In tend laterally at a 450 angle, and the shanks captivity the sex call is sounded only occa- are turned inward at the same angle, forming sionally. a diamond-shaped enclosure in which the When the back of the male is touched at a eggs are deposited. point just caudal to the axillae, a vocaliza- As the female assumes the oviposition pos- tion is generally emitted which is known as ture, the male moves forward slightly and ro- the warning croak. It can be described as "ir- tates the shanks of his hind limbs somewhat a-a-a-h----ir-a-a-h---ir-a-a-h---," etc., which downward and inward. continues as long as the stimulation of the The female starts the oviposition by a back is maintained. The anestrous female sharp abdominal contraction followed by a also emits a warning croak when her back is concave arching of her back. The male re- touched, but the female's warning vocaliza- sponds to these movements by spreading his tion is not so loud as that of the male. When legs slightly and arching his back convexly one male attempts to clasp another male or (upstroke), followed by a down stroke in an anestrous female, the frog being clasped which he straightens out his arched back and emits the warning croak as soon as its back is presses his legs against the female's abdomi- touched, and this response is partially re- nal walls. We have termed this complex se,- sponsible for the clasping male's prompt re- ries of motions of the male an "ejaculatory" lease. This is one of two major factors which or "spawning" movement. With each of these prevent males from remaining in amplexus ejaculatory movements, a cluster of eggs is with other males or with anestrous females. emitted from the female's cloaca and sperm The second factor is the relative girths of the are ejected from the male's cloaca. There are slender male and spent female as contrasted on the average 16 spawning movements dur- to the swollen size of the egg-laden estrous ing each egg laying, but in individual cases female. The larger the girth of the clasp ob- the total may vary from 10 to 23. The mean ject (within certain limits) the more likely is duration of the oviposition is about four min- the clasping male to retain his clasp. utes, with a range of two to eight minutes. The sexually active male attempts to clasp After all the eggs are deposited, the male a male, female, or any object of the approx- usually swings his hind limbs from side to imate size and shape of a frog. There is little side (pre-release motions) and finally releases discrimination in these attempts among the female on one or the other side. After the males, anestrous females, estrous females, or spawning is terminated and the female aban- pairs. If an estrous female is clasped, am- dons the egg-laying posture, she generally plexus is maintained until the oviposition is moves away from the eggs. In most cases the completed. Amplexus is pectoral, with the male's release of the female occurs within one ventral surface of the male pressed closely minute after the end of oviposition.

97 MAJOR NUCLEAR MASSES OF THE FROG BRAIN

THE HISTOLOGICAL DETAILS of the anuran The cerebral hemispheres are divided brain have been described by a large number through most of their rostrocaudal extent in- of investigators, and two of these studies to a dorsally situated pallium and a ventral (Herrick, 1921, 1925) were based partly on subpallium by cell-free medial and lateral Rana pipiens material. However, the infor- zona limitantes (figs. 1 to 3, z. lim. m. and z. mation is quite scattered, the terminology lim. 1.) and their corresponding ventricular employed by the various investigators varies and external sulci (figs. 1 to 3, s. lim. hip., s. considerably, and the illustrations are not endorh., s. sep. pall., and s. lim. lat.). The particularly suitable for the present study. medial segment of the pallium is known as For these reasons it has been considered ad- the primordium hippocampi (figs. 1 to 5, prim. visable to present a brief review of the major hip.), the lateral segment as primordium piri- nuclear masses in the forebrain, diencepha- forme (figs. 1 to 5, prim. pir.). Dorsally there lon, and midbrain of the leopard frog. is situated the primordium palli dorsalis (figs. In the following descriptions we have at- 1 to 5, prim. pall. d.). In Rana pipiens this tempted to adopt the most widely accepted condensation of cells cannot be sharply de- terminology. In general it follows that of limited from the primordium hippocampi Herrick (1933) and of AriEns Kappers, Hu- medially, or the primordium piriforme lat- ber, and Crosby (1936). The descriptions and erally. illustrations are based on a cross-section se- The septum comprises the medial sector of ries cut at 15 ,u and stained with gallocyanin subpallium and is readily divisible into me- (Einarson, 1932). dial and lateral septal nuclei (figs. 1 and 2, n. The reader is referred to the two volumes sep. m., n. sep. 1.). The extension of the sep- by Aritns Kappers, Huber, and Crosby (1936) tum caudal to the interventricular foramen for a more detailed discussion of the anuran is known as the pars fimbrialis septi (fig. 3, brain and for an excellent review of the liter- fim. sep.). ature. The lateral sector of the subpallium has The forebrain consists of two cerebral hem- been subdivided in two different ways. ispheres and an unevaginated telencephalon Rdthig (1912), AriEns Kappers and Hammer medium. At the frontal end of each cerebral (1918), Ari6ns Kappers (1921), and others hemisphere are situated the olfactory bulbs recognize a paleostriatum and a more dor- which can be delimited from the remaining sally situated epistriatum. Herrick (1921) hemispheres by a sulcus limitans bulbi olfac- following the lead of Gaupp (1899) considers torii. the rostral part of the lateral sector of the

FIG. 1. Transverse section through the middle of the cerebral hemispheres of Rana pipiens; gallocyanin; X24. (All sections cut at 15A.) 98 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 99 subpallium to be the primordium of the cor- The small masses of cells, oval in cross sec- pus striatum, while the more caudally lying tion, are known as the bed nuclei of the hip- cell group at the level of the interventricular pocampal commissure (figs. 3 and 4, n. hip. foramen' is designated as the homologue of com.). the mammalian amygdala. However, Herrick The ventral aspect of the diencephalic-te- (1921) does carry a few strands of cells of the lencephalic boundary is not clearly defined. corpus striatum to the same caudal level. Some authors consider the preoptic area to be Herrick (1933, p. 164) points out that his part of the telencephalon, and place the ven- subdivisions of the ventrolateral quadrant of tral di-telencephalic boundary at the dorsal the hemisphere overlap those of Aridns Kap- ridge of the chiasma. Others regard this re- pers. However, it seems possible from a gion as diencephalic, placing the ventral di- purely topographical point of view to recog- telencephalic boundary at the anterior com- nize three more or less discrete areas, namely, missure. In the present report we shall follow a rostrally lying corpus striatum or paleo- Herrick (1933) and place the preoptic area striatum (figs. 1 and 2, corp. str.), a dorsal "somewhat arbitrarily" in the telencephalon, epistriatum (figs. 1 and 2, epistr.), and a cau- bearing in mind, as Herrick does, the func- dal amygdala (fig. 3, amyg.). tional relationship of the preoptic area with The medial forebrain bundle (figs. 1 to 6, the diencephalon.

FIG. 2. Transverse section through the anterior part of the preoptic area of Rana pipiens; gallocyanin; X24.

m. f. b.), the lateral forebrain bundle (figs. The structure of the preoptic area of Rana 1 to 6, 1. f. b.), and three major components pipiens follows the description of Crosby and of the anterior commissure can be clearly Woodburne (1940) for Rana catesbeiana. The recognized in gallocyanin-stained material. condensation of cells surrounding the pre- The major subdivisions of the anterior com- optic recess (rec. preop.) is known as the nu- missure are (1) the hippocampal commissure cleus preopticus and is composed of three (fig. 3, hip. com.), (2) the decussation of the subdivisions, namely, a periventricular part medial forebrain bundle (figs. 2 and 3, dec. m. (figs. 2 and 3, n. preop. peri.), a medial part f. b.), and (3) the decussation of the lateral (figs. 2 and 3, n. preop. m.), and a magno- forebrain bundle (fig. 3, dec. 1. f. b.). Asso- cellular part (fig. 3, n. preop. mag.). In Rana ciated with each of the two decussations just pipiens the pars magnocellularis is markedly mentioned are condensations of cells known as reduced both in size and differentiation when the bed nuclei of the respective decussations compared with Rana catesbeiana or R. clami- (figs. 2 and 3, n. dec. m. f. b., n. dec. 1. f. b.). tans. Its cells are only slightly larger than the 100 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86

prim. hip.lt prim. pir. S. sep. poll.

im.M.~~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

V..I,k~~ ~~~~~~~~~n ec . .b f.tbi.ep

ne ..f. b. n Op .m

p e o ma f reop. d.n p. eb.

n. preop. per.

rec. preop.

FIG. 3. Transverse section through the anterior commissure of Rana pipiens; gallocyanin; X 24. adjacent cells of the nucleus preopticus peri- lon. When, in our experiments, the preoptic ventricularis and nucleus preopticus medi- area was ablated from its anterior edge as far alis. Following Crosby and Woodburne caudally as the rostral edge of the chiasma, (1940), we have designated the fibrous area we classified the destruction as a complete and scattered cells lateral to the preoptic nu- ablation of the preoptic area. clei as the lateral preoptic area (figs. 2 and 3, The diencephalon is divisible into four ma- a. preop. 1. or a. preop. lat.). jor components, namely, the epithalamus, It should be noted that the preoptic nu- the dorsal thalamus, the ventral or subthala- cleus extends caudally over the chiasma to mus, and the hypothalamus. In cross sec- its dorsal tip where the nucleus preopticus tions, the limits of these regions are clearly merges with the nucleus suprachiasmaticus marked by ventricular sulci (figs. 5 to 7,s. of the hypothalamus. In the experiments subhab., s. med., s. vent.). here reported, we have considered this edge The epithalamus consists of the pineal of the preoptic area between the anterior and stalk and associated structures, the habenu- dorsal edges of the chiasma as a transitional lar commissure (fig. 6, hab. com.), the haben- zone between telencephalon and diencepha- ular nucleus (fig. 6, n. hab.), and the sub-

FIG. 4. Transverse section through the emenentia thalami of Rana pipiens; gallocyanin; X24. 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 101

s. subhob. s. med. -n. dor. thal. ext - n. dor. thal. int. n. vent. thal. *n. gen. lot. nur. n. gen ,iat. n. suproch

FIG. 5. Transverse section through the anterior part of the diencephalon of Rana pipiens; gallocyanin; X 24. habenular nucleus (figs. 5 and 6, n. subhab.). posterior portions are easily separated into a The dorsal thalamus is divisible into ante- pars interna (figs. 5 to 7, n. dor. thal. int.) in rior, middle, and posterior portions. The an- which the cells are arranged in a somewhat terior portion contains the nucleus of Bel- linear fashion, and a more scattered pars ex- lonci (figs. 4 and 5, n. Bell.), the nucleus terna (figs. 5 to 7, n. dor. thal. ext.). At the geniculatus lateralis (fig. 5, n. gen. lat.), and caudal end of the dorsal thalamus a pretectal two concentrations of neuropil associated area (fig. 8, a. pret.) and a nucleus of the pos- with the foregoing nuclei (fig. 5, n. Bell. neur., terior commissure (fig. 9, n. post. com.) can n. gen. lat. neur.). These collections of neu- be identified. ropil are faintly seen in sections stained for The emenentia thalami (fig. 4, em. thal.) cellular detail. The boundary between the which is the most rostral portion of the middle portion (figs. 5 and 6) and posterior diencephalon is recognized as an anterior ex- portion of the dorsal thalamus (fig. 7) is not tension of the ventral or subthalamus. The easily recognized in transverse sections. The cellular concentrations of the subthalamus cellular concentrations in the middle and are also divisible into a linearly arranged pars

FIG. 6. Transverse section through the middle of the diencephalon of Rana pipiens; gallocyanin; X24. 102 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86

FIG. 7. Transverse section through the posterior part of the diencephalon of Rana pipiens; gallocyanin; X24. interna (figs. 6 and 7, n. vent. thal. int.) and by the intrahypothalamic sulcus (fig. 7, s. a scattered pars externa (figs. 6 and 7, n. intrahyp.). vent. thal. ext.). Crosby and Woodburne (1940) recognize a The most anterior component of the hypo- number of subdivisions of these hypothalamic thalamus is the nucleus suprachiasmaticus areas in Rana catesbeiana. Since these com- (figs. 4 to 6, n. suprach.). As already stated, ponents are not easily discernible in Rana this nucleus is continuous rostrally with the pipiens, they need not be considered further. preoptic nucleus. The nucleus suprachiasmat- The mesencephalon consists of the tectum icus is replaced caudally by the pars ven- opticum or superior colliculi (figs. 7 to 12, tralis hypothalami (figs. 6. to 8, vent. hyp.). tect.), the inferior colliculi or tori semicircu- Farther caudally, the pars dorsalis hypo- lares (figs. 10 to 12, inf. col.), and ventrally thalami (fig. 7, dor. hyp.) intervenes between the tegmentum (figs. 8 to 12, teg.). the ventral thalamus and the pars ventralis Huber and Crosby (1933, 1933a) recognize hypothalami and is separated from the latter six fundamental layers in the vertebrate tec-

FIG. 8. Transverse section through the anterior end of the tectum mesencephalicum of Rana pipiens; gallocyanin; X24. 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 103

FIG. 9. Transverse section through the posterior commissure of Rana pipiens; gallocyanin; X24. tum. In the tailless Amphibia, according to trigeminus (figs. 8 and 9, n. mes. V) are rec- Ariens Kappers, Huber, and Crosby (1936) ognized. there are recognized (labeled in fig. 8): (1) Caudal to the inferior colliculi, the gan- stratum opticum (str. op.), (2) stratum fibro- glion isthmi (fig. 12, gang. isth.) is easily iden- sum et griseum superficiale (str. sup.), (3) tified by its border of deeply staining cells. In stratum griseum centrale (str. gr. cent.), (4) the tegmentum, the large cells of the oculo- stratum album centrale (str. alb. cent.), (5 motor nucleus (figs. 8 and 9, n. N. III) can be and 6) stratum griseum periventriculare in- delimited from the similarly appearing cells of termingled with fibers of the stratum fibro- the trochlear nucleus (fig. 10, n. N. IV) by a sum periventriculare (str. peri.). Towards region relatively free of large motor cells. At the anterior end of the tectum the large scat- the anterior level of the oculomotor nucleus, tered cells of the nucleus mesencephalicus the nucleus opticus tegmenti (fig. 8, n. op.

FIG. 10. Transverse section through the anterior part of the inferior colliculus of Rana pipiens; gallocyanin; X 24. 104 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86

n. int. hyp.

FIG. 11. Transverse section through the interpeduncular nucleus of Rana pipiens; gallocyanin; X24. teg.) can be identified. Farther caudally, the peduncular nucleus (fig. 11, n. int.) is situ- nucleus lateralis profundus (fig. 9, n. lat. ated along the midline near the caudal end of pro.) is seen to be embedded in the fiber bun- the tegmentum. dles of the cerebral peduncles. The inter-

FIG. 12. Transverse section through the ganglia isthmi of Rana pipiens; gallocyanin; X24. EXPERIMENTAL PROCEDURES AND RESULTS

SWIMMING RESPONSE OF THE jection and were operated upon the day be- MALE TO THE FEMALE fore the observations began. The controls (intact males) were given a THE MALE FROG'S TENDENCY to swim towards two-hour test with the estrous females. If and attempt to embrace a female was tested they showed the response by swimming over in aquaria 30 cm. by 40 cm. by 25 cm. filled to the female and clasping her, they were with 10 cm. of water at approximately 230 C. forcibly separated after two to five minutes Estrous (fully ovulated) females, to be used and were retested. The operated frogs were as clasp objects, were obtained by injecting similarly tested for two hours. In most cases, the females two or three days prior to the if they did not show the reaction, the test was test with two female pituitaries. These fe- continued for an additional period, generally males were placed at random in the test tanks two more hours. In some instances when the with the experimental males. operates did not show the response, they were The control males were injected with a fe- given a second pituitary injection and were male pituitary one day before being tested. retested on the following day. With few ex- Most of the experimental males received the ceptions, those that did not react during the pituitary treatment on the day preceding the first two hours failed to exhibit the response operation, and tests were started approxi- during the additional time allowed them. mately one hour after the surgical treatment. Table 1 summarizes the results of this ex- A few of the males received the pituitary in- periment. The percentages of males exhib-

BLE 1 EFFECTS OF BRAIN INJURY UPON THE SWIMMING RESPONSE OF OPERATED MALES TO OVULATED FEMALES

| |No. of Percentage No.Nooff Males of Males Record Numbers of Operated Operation Males Exhibiting Exhibiting Males' Tested Swimming Swimming Response Response Not Response' Response Exhibited Exhibited Intact males (controls) 24 23 95.9 Extensive injury to forebrain. 11 10 90.9 63, 65, 67, 742, 813, 75 Preoptic areas intact 910, 915, 929, 935, 942 Forebrain ablated, excepting the 10 10 100.0 2, 8, 12, 51, 58, 68, preoptic area 70, 79, 92, 125 Forebrain ablated excepting cau- 13 7 53.8 32, 48, 60, 89, 104, 78, 82, 95,96,98,1;20 dal three-fourths to one-quarter 105, 120, 939 of the preoptic area Forebrain completely ablated (in- 19 5 26.3 52, 119, 121,127, 140 46,49, 55, 72, 73, 76, cluding from 75% to 100% of 77, 83, 84, 94, 103, the preoptic area) 106, 115, 155 Preoptic area ablated or exten- 12 10 83.3 11, 16, 17, 62, 215, 74, 80 sively injured 918, 920-923 Hypothalamus mostly ablated 9 7 77.8 85, 88, 93, 97, 831, 86, 91 906, 924 1 At least once during the test period. 2 For descriptions of the individual operations and summaries of the behavioral data, see page 117. 105 106 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 iting the swimming reaction after (1) exten- trous females did not differ significantly from sive injury to the forebrain, leaving the pre- the controls (less than twice the standard optic area intact; (2) complete ablation of error). the forebrain with the exception of the pre- The conclusion which is drawn from these optic area; and (3) ablation or extensive data is that complete loss of the forebrain injury to the preoptic area, leaving the rest of (including the preoptic area) causes a consid- the forebrain intact, did not differ signifi- erable reduction in the number of males cantly from the controls. The per cent differ- that will swim towards and clasp the es- ences between the controls and operates are trous female. If, on the other hand, the cere- less than twice the standard error. bral hemispheres alone are extirpated (leav- When the forebrain was ablated, including ing the preoptic area intact) or the preoptic from 75 per cent to all the preoptic area, only area is removed (leaving the cerebral hemi- 26.3 per cent of the males responded, the de- spheres intact), a normal swimming reaction viation from the record of the controls being is exhibited. Finally, loss of most of the hypo- clearly significant. When the forebrain was thalamus does not appear to affect the swim- extirpated with the exception of the caudal ming response. three-quarters to one-quarter of the preoptic Removal of the preoptic area in addition to area, 53.8 per cent of the operates showed the the cerebral hemispheres often resulted in response. This difference is probably reliable some injury to the anterior edges of the dor- since it is greater than two and one-half times sal thalamus, ventral thalamus, and epithal- the standard error. This group consisted of amus. However, we were unable to correlate operates which were intermediate as regards the loss of the swimming reaction with the ex- the amount of preoptic area removed with tent of the diencephalic injury. It should be the cerebral hemispheres; the percentage of understood that this does not eliminate the males exhibiting the swimming response also possibility that injury to the thalamus or fell into intermediate position. epithalamus might affect the swimming re- Following complete removal of the hypo- sponse adversely. thalamus, and after complete ablation or ex- On the other hand, in those operations in tensive injury to the preoptic area, the per- which the preoptic area was spared, remnants centages of males that reacted to the es- of the cerebral hemispheres and varying

tectum inferior colliculus thalomus

hypophysis hypothalamus

FIG. 13. Diagrammatic sagittal section through the brain of Rana pipiens. The regions situated anterior to the heavy broken line were explored while studying the swimming reaction of the male towards the estrous female. Either the preoptic area (delimited by oblique cross hatching) or the remainder of the cerebral hemispheres (delimited by horizontal cross hatching) must remain intact if this behavior is to be elicited readily. 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 107 amounts of the anterior commissure and re- reaction will have to be determined by fur- lated bed nuclei sometimes remained. In ther experimentation. these cases no relation was found between the Figure 13 illustrates the areas of the brain extent of the remaining cerebral tissue and that were explored in this experiment (an- the swimming reponse to the estrous female. terior to the heavy broken line) and the por- Whether the presence of the anterior com- tions that appear to be essential for the missure or slight cerebral remnants, or inva- mediation of the swimming reaction of the sion of the diencephalon alters the swimming male towards the estrous female. Either the

TABLE 2 EFFECTS OF BRAIN INJURY UPON THE WARNING CROAK OF THE MALE No. of Percent- Record Numbers of Operated Males' Males Males of Operation Tested Re- IageMales Re- Response Response Not spondingj sponding Exhibited Exhibited - Intact males (controls) 25 25 100.0 Forebrain ablated 20 20 100.0 20, 24, 34, 46,47,49, 50, 52,103,106,115, 121, 123, 126'-128, ----I----135,140,- 143,.322. Hypothalamus mostly ablated 8 8 100.0 85,97,344,403,831, 845, 924, 945 Forebrain and thalamus extirpated 10 9 90.0 53,54, 108, 341,412, 402 413, 422, 741, 911 Thalamus ablated, plus extensive in- 11 11 100.0 100, 112, 114, 116- jury to posterior third of forebrain 118, 324, 331, 743, 805, 815 Forebrain and diencephalon ablated. 2 2 100.0 411,433 Tecta largely ablated; tegmentum invaded; slight injury to inferior colliculi Extensive injury to tecta. Slight inva- 3 3 100.0 212,304,333 sion of inferior colliculi. Two operates included ablation of cerebellum Extensive injury to tegmentum. Three 4 3 75.0 724,832,928 704 included ablation of hypothalamus

Forebrain and diencephalon ablated. 13 0 0.0 242, 414, 424, 431, Tecta and inferior colliculi ablated 441, 443, 521, 531, or mostly ablated. Lesions extended 532, 712, 722, 723, into tegmentum. Two operates in- 731 cluded ablation of cerebellum

Tecta and inferior colliculi largely 11 1 9.1 241 45, 101, 214, 233, ablated. Three operates included 311-314, 321, 903 damage to thalamus. Two included ablation of cerebellum

Extensive lesions in hypothalamus, in- 4 0 0.0 711, 714, 721, 733 ferior colliculi, and tecta

For descriptions of the individual operations and summaries of the behavioral data, see page 117. 108 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOIJ. 86 tectum inferior colliculus tholamus

gonglion isthmi

hypophysis' hypothatomus preoptic area FIG. 14. Diagrammatic sagittal section through the brain of Rana pipiens. The regions situated anterior to the heavy broken line were explored while studying the warning croak. The cross-hatched area delimits the inferior colliculi which must remain intact if this behavior is to be elicited. cerebral hemispheres (horizontal cross-hatch) In figure 14 the cross-hatched area repre- or the preoptic area (oblique cross-hatch) sents the region of the frog brain which ap- must remain intact if this response is to be pears to be necessary for the mediation of the elicited readily. warning croak. The regions that were explored in this study are anterior to the heavy EMISSION OF THE WARNING CROAK broken line. The warning croak was elicited readily by The record of operated male 433 (fig. 23) touching the back of the male with the illustrates the persistence of the warning thumb and forefinger at a point just caudal croak following a transection through the to the axillae. In the control group, the re- midbrain at a level just rostral to the nuclei sponse occurred an average of 1.6 seconds of the oculomotor nerve with the tecta com- after the application of the stimulus, and all pletely ablated, but with only slight damage the 25 control males responded within seven to the inferior colliculi. The performance of seconds. male 314 (fig. 21) exemplifies the abolition of In testing the operated males for the warn- the warning croak following the removal of ing croak, each animal was stimulated con- most of the tecta and the entire inferior tinuously for at least five minutes. Frogs that colliculi. Results obtained with male 928 failed to croak were given a brief rest period, (fig. 26) are an example of extensive hypo- and were then retested at least once more. thalamic and tegmental injury which did not The results of this experiment are summa- interrupt the warning croak. The operation rized in table 2. Examination of this table re- of male 901 (not included in table 2) con- veals that complete forebrain and dience- sisted of a midsagittal incision from the me- phalic extirpation did not interfere with the dulla oblongata to the dorsal thalamus. This response. Similarly, after extensive injury or lesion did not abolish the warning croak. In ablation of the tectum and cerebellum, the operated male 711, the destruction of the in- response could still be obtained, even when ferior colliculus on one side only was sufficient the lesions extended a considerable distance to abolish the warning croak. into the tegmentum. Slight injury to the inferior colliculi (tori semicirculares) did not in- SEX CALL terrupt the warning croak. However,with only When Rana pipiens are kept in captivity, one exception, operations involving extensive very few males emit the sex call, although injury to the inferior colliculi abolished this this limited group may call repeatedly over a response completely. period of several hours. In our experiments 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 109 homoplastic pituitary injections increased sexually active male, it will arch its back, ad- the proportion of calling males, but the group just itself squarely on the back of the female, still appeared to be too small to warrant and remain clasping with a powerful grip. If, quantitative records of the sex call following on the other hand, the male being tested is brain injury. However, some operated males not sexually active, the clasp reflex will cease were heard to sound the sex call, and when- as soon as the experimenter releases the test ever the individual could be definitely iden- animal. tified, the call was recorded. These data ap- Females exhibit this clasping behavior, but pear to be of sufficient interest to be reported the muscular complex involved is consider- here. ably weaker than in the male, thus account- The sex call was heard following various ing for a relatively feeble grip. Occasionally lesions of the forebrain (males 1, 2, 12, 41, 51, females are seen clasping other females 67, 70, 125, 302, 813, 816, 923, 929, and 936), (Noble and Aronson, 1942). Males exhibit after complete ablation of the forebrain (male the clasp reflex throughout the year, but it is 115), and after partial or complete hypo- much weaker immediately after the breeding thalamic injury (males 403, 906, 924, 930, season. Again, this seems to be due, at least 941, 946). The call was also sounded by males in part, to a reduction of the brachial muscu- suffering various diencephalic and midbrain lar apparatus. injuries which did not reach the inferior Males in which the brains had been tran- colliculi (males 109, 212, 801, 815, 822). sected at the level of the cerebellum or ante- Operated male 233 (fig. 20) is a particularly rior end of the medulla oblongata exhibited a interesting case. This male could not be stim- clasping pattern which was considerably dif- ulated to sound the warning croak even after ferent from that just described for the intact numerous repetitions of the test, yet for two animal. The slightest stimulation of the pec- successive days he repeatedly emitted the sex toral skin or ventral surfaces of the forelimbs call. Examination of the brain revealed com- in these operates initiated a strong clasp re- plete ablation of the tecta and inferior collic- flex. Such preparations remained clasping uli with the ganglia isthmi, cerebellum, and one's finger or inanimate objects for long pe- adjacent structures remaining uninjured. riods, the duration of the clasp appearing to While no definite conclusion can be drawn depend on muscular strength rather than on from these data, it does appear that the es- any relaxation of the clasp. Even after the sential mechanism controlling the sex call is clasp object was removed, these operates gen- located somewhere in the midbrain. By the erally held their forelimbs in a clasping posi- process of elimination it is suggested that the tion for some time. This clasping posture ganglia isthmi might form an essential link in ceased as soon as the frog was placed on the this mechanism. substratum. Since the slightest stimulation of the pec- CLASP REFLEX toral skin caused the forelimbs to assume the clasping position, it was usually necessary to Although quantitative measurements of spread the forelimbs apart forcibly when at- the clasp reflex were not taken, qualitative tempting to place the operated male on es- observations of the effects of various inva- trous females. These males did not arch their sions and transections of the brain on this be- backs or attempt to adjust themseves square- havior were noted. In the intact frog, the re- ly on the back of the female, but they held on flex can be demonstrated in two ways. First, tightly in whatever position they were if the pectoral skin and ventral surfaces of placed. If they slid off to one side, as often the frog's forelimbs are gently stroked with happened, no correction was attempted. the fingers, the frog will clasp the fingers and Following transection through the caudal will continue to do so as long as the stroking end of the medulla oblongata (spinal animal), continues. Secondly, if the experimenter the frogs exhibited a similar clasp pattern, grasps a male by the hind limbs and places it and therefore this behavior is referred to as a on the back of an estrous female, the clasp spinal clasp reflex. will occur. If the frog thus manipulated is a Males with forebrain lesions or with com- 110 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 plete ablation of the forebrain showed no de- SPAWNING BEHAVIOR viation from the normal in their clasping behavior. With extensive lesions in thedienceph- To test the spawning behavior of operated alon, the clasp pattern resembled slightly males they were placed on estrous (ovulated) that of the spinal clasp reflex described above. females and were allowed to clasp. The ob- As the lesions were placed farther and farther servations were carried on in aquaria 30 cm. caudally in the midbrain and cerebellum, the by 40 cm. by 25 cm. filled with about 8 cm. of behavior resembled more and more the spinal water at approximately 23° C. The intact clasp pattern. males normally exhibit one spawning move- Thus it appears that invasions of the ment following each oviposition movement of diencephalon, midbrain, cerebellum, and me- the female. In the execution of these spawn- dulla oblongata modify the clasping behav- ing motions, a limited amount of variation is ior to resemble closely that of the spinal frog. seen. If the operated frog responded to all the

TABLE 3 EFFECTS OF BRAIN INJURY UPON THE SPAWNING RESPONSES OF THE MALE Operates Show- ing Normal Record Numbers of Operated Males' No. Av. NO. Spawning Operation Males Showi hoin Tested ings) Percent- Shwng Normal Abnormal per Male No. age of To- Spawning Behavior Spawning tal Tested Behavior Intact males (controls) 37 1.1 37 100.0 Forebrain completely ablated (includ- 13 1.7 13 100.0 34, 46, 47,49, 123, ing from 75% to 100% of the preop- 126-128, 133-135, tic area) 143, 322 Hypothalamus mostly ablated 12 1.9 12 100.0 85, 86, 88, 93, 97, 343, 344, 403, 845, 924, 941, 945 Forebrain and/or thalamus ablated or 7 1.1 7 100.0 14, 53, 413, 801, extensively injured 802, 815, 823 Extensive lesions in tecta and inferior 5 1.0 5 100.0 233, 241, 312, 333, colliculi. Three included ablation of 903 cerebellum Extensive lesion in forebrain, dien- 6 1.0 6 100.0 36, 342, 414, 433, cephalon, and/or midbrain, involv- 734, 832 ing anterior half of tegmentum only Hypothalamus ablated or extensively 6 1.0 0 0.0 542, 702, 713, injured. Extensive invasion of teg- 714, 724, 733 mentum. Two included damage to inferiorcolliculi, tecta, and thalamus Lesion in caudal half of tegmentum 1 2.0 0 0.0 603 Extensive injury or ablation of fore- 10 1.1 1 10.0 311 313, 411, 424, brain, diencephalon, and/or mid- 443, 521, 523, brain. Caudal half or entire tegmen- 532, 712, 731 tum invaded. For descriptions of the individual operations and summaries of the behavioral data, see page 117. 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA III female oviposition movements, and if the ous groups of operates. It will be noted that pattern of these spawning responses resem- the males sustaining midbrain lesions were bled that of the control males, the operate seldom tested more than once, because fol- was classified as exhibiting normal spawning lowing midbrain injury the operates seldom behavior. Among the operates, the distinc- remained in a satisfactory physical condition tion between normal and abnormal responses long enough to warrant successive tests. was very sharp. There was seldom any ques- From these data it can be concluded that tion as to the classification of the spawning neither the forebrain, diencephalon, tecta, reactions of operated individuals. inferior colliculi, nor cerebellum is essential The abnormal responses of the operates for the mediation of normal spawning move- were of three types. In the first group the op- ments. Likewise, the anterior half of the teg- erated males did not respond to all the ovi- mentum to approximately the caudal end of position movements of the female, but when the oculomotor nuclei is not a necessary re- they did react, the ejaculatory movements gion for this reaction. On the other hand, the were comparable to those of the intact ani- posterior tegmentum extending caudally mal. Some of these males started spawning in from the region of the trochlear nucleus must quite a normal manner, but in the midst of be intact if normal spawning behavior is to be the egg laying they ceased to react. Others obtained. did not exhibit any spawning movements un- In table 4 it is seen that those groups of op- til the spawning was well under way, and erates in which the male spawning behavior then completed the oviposition with typical was mostly normal (compare with table 3) ejaculatory motions. In the second group the the per cent of fertile egg masses, as deter- operated males exhibited short, irregular mined by the development of normal em- spawning movements which gave the impres- bryos, varied from 60 to 100 with a mean of ion that only a fraction of the muscular com- 77.5. In those groups of operates in which the plex was being activated. A third group of spawning activity of the male was mostly ab- brain-operated males exhibited no response normal (last three categories of operates in whatever to the oviposition movements of table 4), the per cent of fertile egg clusters the female. varied from 0 to 44.4 with a mean of 21.5. The results of this experiment are summa- The procedure of storing ovulated females rized in table 3. The data for the controls are in the refrigerator for one or more days while taken from a previous study on the normal be- awaiting operated males resulted in an in- havior (Noble and Aronson, 1942). It is creased incidence of partially egg-bound shown that extirpation of the forebrain, frogs (Noble and Aronson, 1942) and un- diencephalon, tecta, inferior colliculi, cere- doubtedly caused a lowered fertility of the bellum, and anterior half of tegmentum (to egg masses. the caudal end of oculomotor nuclei) did not It was a matter of some interest that even interrupt the spawning responses. On the brain-operated males that exhibited extreme- other hand, when the posterior tegmentum ly abnormal mating behavior were still appar- was invaded, the reaction was significantly ently able to emit some sperm. For example, altered or completely abolished in all cases male 714 with an extensive tegmental lesion except one; and in this particular operate, showed no spawning responses at all, but male 311, the tegmental injury caudal to the some of the resulting eggs were fertilized. In posterior end of the oculomotor nuclei was all the other spawnings with males that ex- unilateral. hibited abnormal spawning behavior and Many of the operates participated in two that yielded some fertile eggs, one or more or more egg layings on successive days. The ejaculatory movements were recorded. results were entirely consistent. All the op- The data on male 603 (fig. 24) illustrate a erates showing normal spawning behavior relatively small lesion in the caudal part of during the first ovipositions showed similarly the tegmentum which abolished the mating typical behavior in the succeeding spawnings. response. On the other hand, the records of Column 3 in table 3 indicates the average male 414 (fig. 22) illustrate a very extensive number of spawnings per male for the vari- brain injury which did not modify the spawn- 112 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 TABLE 4 EFFECTS OF BRAIN INJURY TO THE MALE UPON THE EFFICACY OF SPERM EMISSION AS DETERMINED BY THE FERTILITY OF THE EGGS AFTER SPAWNING

eratslizing Record Numbers of Operated Males2 No.lof Egg Clusters' OperationOperation TMaestedTested Percentage Fertilizing Not Fertilizing No. of Total Egg Clusters Egg Clusters Tested Intact males (controls) 7 5 71.4 Forebrain completely ablated (including 8 7 87.5 34, 47, 49, 127, 128, 34, 46 from 75% to 100% of the preoptic 133, 143 area) Hypothalamus mostly ablated 10 6 60.0 85, 86, 88, 343, 344, 403 93, 845, 924, 941 Forebrain and/or thalamus ablated or 5 4 80.0 413, 801, 802, 815 823 extensively injured Extensive lesions in tecta and inferior 4 4 100.0 233, 312, 333, 903 colliculi. Three included ablation of cerebellum Extensive lesion in forebrain, diencepha- 5 3 60.0 36, 414, 832 433, 734 lon, and/or midbrain, involving anterior half of tegmentum only Hypothalamus ablated or extensively in- 5 1 20.0 714 542, 702, 713, 724 jured. Extensive invasion of tegmentum. Two included damage to inferior colliculi, tecta, and thalamus Lesion in caudal half of tegmentum 1 0 0.0 603 Extensive injury or ablation of fore- 9 4 44.4 311, 411, 424, 731 313, 443, 521, brain, diencephalon, and/or mid- 532, 712, 731 brain. Caudal half or entire tegmentum invaded 'As determined by the development of at least one normal embryo. 2 For descriptions of the individual operations and summaries of the behavioral data, see page 117. ing response. The operation consisted of a The lesions in the tegmentum generally transection slightly anterior to the caudal caused severe systemic effects, and frogs with level of the oculomotor nuclei with the tecta such injury were often in poor physiological mostly ablated and the inferior colliculi se- condition. This was due, no doubt, to the verely damaged. proximity of the injury to the cardiac and re- Figure 15 is a diagrammatic sagittal sec- spiratory centers in the medulla oblongata. tion through the frog brain. The areas that Because of this effect, it was not considered were explored in testing for the spawning re- practical to try to test the spawning reaction are situated anterior to the heavy sponses in maLes with medulla lesions. This broken line, and the region in the tegmentum raises the question as to whether the operates that appears to be essential for the media- with posterior tegmental lesions failed to re- tion of the response is delimited by cross- spond to the female's oviposition movements hatching. because of a general physiological failure in- 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 113 inferior colliculus tectum thalamus

cerebral hemisphere

FIG. 15. Diagrammatic sagittal section through the brain of Rana pipiens. The regions anterior to the heavy broken line were explored while studying the ejaculatory movements of the male. Lesions in the caudal half of the tegmentum (indicated by cross hatching) alter or abolish this behavior. stead of t-he disruption of a specific nervous complete transection just anterior to the mechanism directly essential to the behavior first cervical segment, except for some fine in question. fragments on one side. Two facts tend to show that the non- Male 38 was also in good condition after responsiveness of males with posterior teg- the operation and survived two tests. He too mental lesions was not due to excessive de- clasped well, but he did not respond in either bility. First, a number of operates sustaining test to the oviposition activities of the fe- extensive brain injury not involving the pos- males. This operation proved to be a com- terior tegmentum were so weak that they plete unilateral transection at the anterior died within a few minutes after spawning in edge of the first cervical segment. a totally normal manner. This can be taken These data suggest that the failure of the to indicate that if the spawning mechanism operates with posterior tegmental lesions to is not interrupted, a physiologically weak- exhibit normal spawning movements is due ened animal will still respond normally. to a direct disruption of a specific nervous The second answer to this problem was ar- mechanism controlling spawning behavior rived at by transecting the brain at the cau- and is not an aftermath of general physiolog- dal end of the medulla (caudal to the cardiac ical weakness resulting from respiratory and and respiratory centers) and anterior to the cardiac failure. origin of the brachial plexus (first spinal segment). When the lesion was properly placed RELEASE AFTER OVIPOSITION above the nuclei of origin of the first cervical The "release time" was defined as the in- nerves, the clasping reflex was not inter- terval between the time that the female rupted. The transections were accomplished moved out of the oviposition posture and the with a small sharp knife after exposing the male's relaxation of the clasp. When this re- spinal cord. The results follow. lease time was less than six minutes, the re- The first successful operation was male 43. lease was considered normal. Those males He remained in good physiological condition that failed to relax their grip in six minutes for many days. He clasped well, but when the were classified as "not releasing." This six- female began to spawn, male 43 did not ex- minute interval is a somewhat arbitrary hibit any response to the egg-laying move- value. It is based upon earlier studies (Noble ments. Post-mortem examination revealed a and Aronson, 1942) in which the average re- 114 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 TABLE 5 EFFECTS OF BRAIN INJURY UPON THE RELEASE OF THE FEMALE BY THE EXPERIMENTAL MALE AT THE TERMINATION OF OVIPOSITION Males Record Numbers of Operated No. of Av. No. Releasing' Males3 Operation Males of Trials | ______|______per Malel No. Per cent Releasing Not Releasing

Intact males (controls) 37 1.1 32 86.5 Extensive injury to the forebrain, pre- 3 1.3 3 100.0 63, 813, 910 optic area intact Forebrain ablated excepting the pre- 5 2.2 5 100.0 3, 8, 26, 68, 125 optic area Forebrain ablated excepting caudal 8 1.5 4 50.0 27, 29, 39, 41 40, 48, 60, 99 three-fourths to one-quarter of the preoptic area Forebrain completely ablated (includ- 12 1.5 3 25.0 50, 123, 133 34, 47, 49, 126- ing from 75% to 100% of the preop- 128, 134, 135, 143 tic area) Preoptic area mostly ablated (rest of 12 1.6 0 0.0 11, 18, 19, 62, 213, forebrain intact) 215, 223, 301, 302, 920, 922, 923 Bilateral injury to preoptic nuclei 4 4.5 0 0.0 6, 16, 17, 921 Hypothalamus mostly ablated 12 1.4 2 16.7 845, 924 85, 86, 88, 93, 97, 343, 344, 832, 941, 945 Pars ventralis hypothalami mostly 6 1.2 6 100.0 604, 841, 842, ablated, pars dorsalis hypothalami 844, 907, 930 mostly intact A trial equals an oviposition with a gravid female. ' Within six minutes after the termination of the oviposition. 3 For descriptions of the individual operations and summaries of the behavioral data, see page 117.

lease time for a group of intact males was de- carded. The only cases considered are those termined. Since the vast majority of males in in which the female laid a full complement of the present experiment either released within eggs in a normal manner. one minute or remained clasping for an hour Table 5 summarizes the results of brain in- or more, the rather arbitrary six-minute di- jury upon the male's tendency to release the viding line could not seriously influence the female at the termination of the oviposition. data. It will be seen that extensive injury or extir- As already noted the method of storing pation of the forebrain leaving the preoptic ovulated females in the refrigerator until they area intact did not affect the release. Because were needed sometimes resulted in partial of the smallness of the samples the increase egg-boundness. Since one of the factors caus- is probably not significant. The 13.5 per cent ing the male to release at the termination of difference between these groups of operated the oviposition is the reduction in the females and the controls is less than two and male's girth resulting from the expulsion of one-half times the standard error. the eggs, the release data on spawnings with When the caudal three-quarters to one- partially egg-bound females have been dis- quarter of the preoptic area was ablated to- 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 115 gether with the forebrain, the number of the anterior commissure. There was no indi- males releasing was reduced to 50 per cent. cation that the survival of cerebral remnants When the forebrain was completely ablated or the invasion of the diencephalon had any (leaving intact less than a quarter of the pre- significant influence on the release behavior. optic area), the number releasing was still The record of male 34 (fig. 18) illustrates a further reduced. When the preoptic area completely decerebrate male which did not alonewas ablated, leaving the rest of the fore- release. Note particularly in figure 18c the de- brain intact, none of the males released. Fi- struction of the epithalamus. In male 8 (fig. nally, after lesions in the preoptic nucleus 18), the cerebral extirpation left the preoptic which spared the remainder of the preoptic area untouched. Slight remnants of the hemi- area, four males failed to release. spheres remained. This male released im- When the pars ventralis hypothalami was mediately (release times less than one largely extirpated, leaving the pars dorsalis minute) in three separate spawnings. The re- intact, release was not affected, but complete sults obtained with male 213 (fig. 19) illus- hypothalamic extirpation interrupted the re- trate the ablation of the preoptic area, leav- lease behavior in most of the cases. ing the rest of the brain intact. This male Column 3 of table 5 indicates the average did not release. number of trials for the various groups of op- The records of males 15 and 918 were not erates. Each trial represents the observation included in the tables but are of some inter- of the release time following one spawning est. The operation on male 15 was a small with a different gravid female. With only a unilateral lesion in the left lateral preoptic few exceptions, the operated males were con- area and extending into the tip of the left sistent in their release behavior when they preoptic nucleus. In six ovipositions the male were subjected to multiple trials. released three times and remained clasping on Just as in the experiment on the swimming the other three occasions. In male 918 (fig. response, complete forebrain extirpation of- 25) the preoptic area of one side was largely ten resulted in slight invasions of the dien- ablated. In four egg layings this male re- cephalon, while the cerebral extirpations spar- leased twice and remained clasping on the ing the preoptic area sometimes left remnants other two occasions. These two records sug- of the hemispheres and varying amounts of gest that unilateral invasion of the preoptic tectum inferior colliculus thalamus

I 141r10,rp-I i Wpars, dorsalisl hypotholamus {pars pars venfralisIntais

FIG. 16. Diagrammatic sagittal section through the brain of Rana pipiens. The regions anterior to the heavy broken line were explored while studying the release of the female by the male at the termination of oviposition. Following lesions in the preoptic area or pars dorsalis hypothalami (indicated by cross hatching), males fail to release the female when the spawnings terminate. 116 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 area will reduce the probability of the male's male at the termination of the oviposition. It releasing the female after oviposition to about is highly probable that some part of this 50 per cent. This is in contrast with unilat- mechanism is located in the rostral part of eral destruction of the inferior colliculus the preoptic nucleus. which abolished the warning croak, and uni- Figure 16 is a diagrammatic sagittal sec- lateral transection through the cervical cord tion through the frog brain illustrating the which abolished the ejaculatory movements. regions explored in this experiment (located It is concluded from these data that the anterior to the heavy broken line) and the preoptic area, and the pars dorsalis hypo- areas which must remain intact (delimited by thalami which appears morphologically as a cross-hatching) for the proper functioning of caudal extension of the preoptic area, con- the neural circuits controlling the release be- tain an essential link in the neural mechanism havior of the male at the termination of the which mediates the male's release of the fe- oviposition. DESCRIPTION OF THE OPERATED BRAINS AND SUMMARY OF BEHAVIORAL DATA IN THIS SECTION all the operated brains re- MALE 8 (FIG. 17): Cerebral hemispheres ab- ferred to in the foregoing tables and text are lated except ventral remnants at preoptic level. described briefly. A summary of the pertinent Preoptic area intact. Anterior commissure and re- behavioral data follows, and in some in- lated bed nuclei mostly intact. Pars fimbrialis septi largely ablated. Amygdala partly ablated. stances items of behavior not previously men- Oviposition I normal. Release immediate. Eggs tioned are included. The designation of the fertile. Oviposition II normal. Release immediate. ovipositions as "normal" or "abnormal" re- Eggs fertile. Oviposition III normal. Release im- fer to the male's behavior only. The release mediate. Eggs fertile. Warning croak elicited. time indicates the interval between the ter- Swimming response to estrous female observed. mination of the oviposition and the release of MALE 11: Preoptic area ablated except caudal the spent female by the male. For those cases remnants of preoptic nuclei dorsal to chiasma. in which the male continued to clasp for sev- Ventral edges of corpora striata and septal nuclei eral hours after the egg laying, the post- just rostral to preoptic area invaded. Anterior spawning observation interval is given. The commissure mostly interrupted. Oviposition I eggs were counted as fertile if at least one normal. No release in 4 hours. Eggs fertile. Ovi- position II normal. No release in 5 hours. Eggs normal embryo developed. fertile. Warning croak elicited. Swimming reac- Cross-section drawings at critical levels tion to estrous female demonstrated. were made from 10 representative operated MALE 12: Lesion same as male 2. Oviposition I brains. These may be compared with the normal. Oviposition II normal. Oviposition III drawings of the intact pipiens brain (figs. 1 normal. Oviposition IV normal. Eggs fertile. to 12). Warning croak elicited. Sex call heard. Swimming MALE 1: Forebrain ablated except caudal half response to estrous female demonstrated. of preoptic area. Rostral edge of dorsal and ven- MALE 14: Cerebral hemispheres ablated. Pre- tral thalami invaded. Warning croak elicited. Sex optic area intact, except slight invasion of ante- call heard. rior edge. Epithalamus ablated. Dorsal and ven- MALE 2: Forebrain ablated except preoptic tral thalami ablated except caudal remnants of area. Anterior commissure and related bed nuclei dorsal and ventral thalamic nuclei. Oviposition removed. Oviposition normal. Warning croak elic- normal. ited. Sex call heard. Swimming reaction to es- MALE 15: Small lesion in left lateral preoptic trous female observed. area which extended into tip of left preoptic nu- MALE 3: Lesion same as male 2. Oviposition cleus. Oviposition I normal. Released after 2 min- normal. Release immediate. Eggs fertile. Warning utes. Eggs fertile. Oviposition II normal. Release croak elicited. delayed 4 minutes. Eggs not fertile. Oviposition MALE 6: Bilateral lesion in preoptic nuclei. III normal. Release delayed 7 minutes. Eggs not Ventral edges of right corpus striatum and right fertile. Oviposition IV normal. Released in 1 min- septal nuclei slightly damaged. Oviposition I ute. Eggs not fertile. Oviposition V normal. Re- normal. No release in 9 hours. Eggs not fertile. lease delayed i hour. Eggs not fertile. Oviposition Oviposition II normal. No release in 12 hours. VI normal. Release delayed 9 minutes. Eggs not Eggs fertile. Warning croak elicited. fertile.

- t Sep M. -n. Sep. L Sep. -dec. mft b. - corp. str. ft g)reop. preop. pen. ftpreop. mog. -. prep.m. n.preop perm -0Q prop I A 8 C FIG. 17. Three transverse sections of the brain of operated male 8; X9. A. Through the anterior end of the preoptic area. Intact brain tissue extended only 75yt anterior to this level. B. 330, farther caudally through the middle of the preoptic area. C. 345,u caudally through the posterior part of the preoptic area. 117 118 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 MALE 16: Large lesion in preoptic area. Ante- tral thalami, nuclei of Bellonci, and habenular rior commissure intact. Oviposition I normal. nuclei ablated. Warning croak elicited. Eggs fertile. Oviposition II normal. Release de- MALE 26: Cerebral hemispheres ablated. Pre- layed 120 minutes. Eggs fertile. Oviposition III optic area intact except rostral tip. Anterior com- normal. No release in 6 hours. Eggs fertile. Ovi- missure and related bed nuclei ablated. Oviposi- position IV normal. No release in 7 hours. Eggs tion I normal. Release immediate. Eggs fertile. fertile. Oviposition V normal. No release in 5 Oviposition II normal. Release immediate. Eggs hours. Eggs fertile. Oviposition VI normal. Re- not fertile. Warning croak elicited. lease delayed 1 hour and 48 minutes. Eggs not MALE 27: Cerebral hemispheres ablated. Cau- fertile. Oviposition VII normal. No release in 5 dal third of preoptic area intact. Anterior commis- hours. Eggs not fertile. Oviposition VIII normal. sure and related bed nuclei extirpated. Habenular Release delayed 10 minutes. Eggs not fertile. nuclei invaded. Oviposition normal. Release im- Warning croak elicited. Swimming reaction to mediate. Eggs not fertile. Warning croak elicited. estrous female demonstrated. MALE 29: Cerebral hemispheres ablated. Cau- MALE 17: Large lesion in preoptic area. Ante- dal half of preoptic area intact. Anterior commis- rior commissure and related bed nuclei invaded. sure and related bed nuclei extirpated. Emenentia Oviposition I normal. No release in 3 hours. Eggs thalami, rostral edges of dorsal and ventral tha- fertile. Oviposition II normal. No release in 6 lamic nuclei, nuclei of Bellonci, and habenular nu- hours. Eggs fertile. Oviposition III normal. Re- clei invaded. Oviposition normal. Release imme- lease delayed 3 hours. Eggs not fertile. Oviposi- diate. Eggs fertile. tion IV normal. No release in 7 hours. Eggs not MALE 32: Cerebral hemispheres ablated. Cau- fertile. Warning croak elicited. Swimming reac- dal third of preoptic area intact. Anterior commis- tion to estrous female demonstrated. sure and related bed nuclei extirpated. Warning MALE 18: Preoptic area ablated. Nucleus su- croak elicited. Swimming reaction to estrous fe- prachiasmaticus hypothalami invaded. Anterior male demonstrated.

A B C FIG. 18. Three transverse sections of the brain of operated male 34; X9. A. Through the caudal edge of the preoptic nuclei. Intact brain tissue extended less than 150,u anterior to this level. B. 255,u farther caudally through the emenentia thalami. C. 240/A caudally through the anterior part of the thalamus. commissure and related bed nuclei mostly re- MALE 34 (FIG. 18): Forebrain ablated except moved. Oviposition I normal. No release after 5 caudal remnants of preoptic nuclei dorsal to the hours. Eggs fertile. Oviposition II normal. No re- chiasma. Emenentia thalami mostly ablated. Nu- lease after 6 hours. Eggs fertile. Oviposition III clei of Bellonci and lateral geniculate nuclei ex- normal. No release after 4 hours. Eggs not fertile. tensively injured. Anterior edges of habenular Warning croak elicited. nuclei invaded. Oviposition I normal. Release de- MALE 19: Preoptic area ablated excepting the layed 3 hours. Eggs not fertile. Oviposition II nor- dorsal edge, and the preoptic nuclei dorsal to the mal. Eggs fertile. Warning croak elicited. chiasma. Oviposition I normal. No release after 4 MALE 36: Transection at caudal end of oculo- hours. Eggs fertile. Oviposition II normal. No re- motor nucleus. Tecta and inferior colliculi com- lease after 6 hours. Eggs fertile. Oviposition III pletely ablated. Oviposition normal. No release in normal. Eggs not fertile. Oviposition IV normal. 6 hours. Eggs fertile. Released after 25 minutes. Eggs not fertile. Warn- MALE 39: Cerebral hemispheres ablated. Cau- ing croak elicited. dal two-thirds of preoptic area intact. Anterior MALE 20: Forebrain ablated except caudal end commissure and related bed nuclei extirpated. of preoptic nuclei dorsal to chiasma. Emenentia Emenentia thalami, anterior edges of the dorsal thalami invaded. Warning croak elicited. and ventral thalamic nuclei, the nuclei of Bel- MALE 24: Forebrain completely ablated. Eme- lonci, and the habenular nuclei invaded. Oviposi- nentia thalami, anterior edges of dorsal and ven- tion I normal. Release immediate. Eggs not fer- 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 119 tile. Oviposition II normal. Release immediate. MALE 52: Forebrain and epithalamus ablated. Warning croak elicited. Considerable injury to dorsal and ventral thal- MALE 40: Cerebral hemispheres ablated. Cau- ami. Small lesion extended to caudal end of thal- dal third of preoptic area intact. Anterior com- amus. Warning croak elicited. Swimming reaction missure and related bed nuclei invaded. Oviposi- to estrous female observed. tion normal. Release delayed 1 hour. Eggs fertile. MALE 53: Forebrain completely ablated. Ep- Warning croak elicited. ithalamus ablated. Dorsal and ventral thalami MALE 41: Cerebral hemispheres ablated. Cau- ablated except caudal edges of dorsal and ventral dal two-thirds of the preoptic area intact. Ante- thalamic nuclei. Pretectal nuclei and nuclei of the rior commissure and related bed nuclei invaded. posterior commissure intact. Oviposition normal. Oviposition I normal. Release immediate. Eggs Warning croak elicited. fertile. Oviposition II normal. Release delayed 4 MALE 54: Forebrain ablated except caudal end minutes. Eggs fertile. Oviposition III normal. Re- of preoptic nuclei dorsal to chiasma. Dorsal thala- lease immediate. Eggs fertile. Warning croak elic- mus, ventral thalamus, and epithalamus ablated. ited. Sex call heard. Slight invasion of anterior edges of the tecta. MALE 45: Tecta ablated except ventro-lateral Warning croak elicited. Swimming response to edges. Inferior colliculi ablated except along ven- estrous female observed. tral edge. Extensive damage to dorsal and ventral MALE 55: Lesion same as male 24. Swimming thalami. Slight invasion of cerebral hemispheres. reaction to estrous female not demonstrated. Warning croak could not be elicited. MALE 58: Lesion same as male 2. Warning MALE 46: Forebrain ablated except caudal croak elicited. Swimming reaction to estrous fe- remnants of preoptic nuclei dorsal to chiasma. male noted. Emenentia thalami, nuclei of Bellonci, and haben- MALE 60: Cerebral hemispheres ablated. Cau- ular nuclei ablated. Oviposition I normal. Eggs dal half of the preoptic area intact. Anterior com- not fertile. Oviposition II normal. Eggs not fer- missure and related bed nuclei extirpated. Ovi- tile. Warning croak elicited. Male did not exhibit position normal. Release delayed j hour. Eggs swimming response to estrous female. fertile. Warning croak elicited. Swimming re- MALE 47: Forebrain completely ablated except action to estrous female demonstrated. caudal end of nucleus preopticus dorsal to chi- MALE 62: Preoptic area completely ablated. asma. Emenentia thalami, nuclei of Bellonci, lat- Nucleus suprachiasmaticus hypothalami invaded. eral geniculate nuclei, and rostral edge of dorsal Slight damage to ventral edges of septal nuclei and thalamic nuclei ablated. Habenular nuclei mostly corpora striata just rostral to preoptic area. Ante- ablated. Oviposition normal. No release after 4 rior commissure and related bed nuclei mostly hours. Eggs fertile. Warning croak elicited. ablated. Oviposition I normal. No release after 2 MALE 48: Cerebral hemispheres ablated except hours. Eggs fertile. Oviposition II normal. No re- remnants of posterior poles. Caudal half of pre- lease after 1 hour. Eggs not fertile. Warning croak optic area intact. Anterior commissure and re- elicited. Swimming reaction to estrous female ob- lated bed nuclei intact. Slight invasion of anterior served. edge of thalamus. Oviposition I normal. Released MALE 63: Cerebral hemispheres removed from in 20 minutes. Eggs not fertile. Oviposition II nor- posterior poles to a level just rostral to the ante- mal. Released after 3 hours. Eggs not fertile. rior commissure. Anterior commissure and re- Warning croak elicited. lated bed nuclei invaded. Preoptic area intact. MALE 49: Forebrain completely ablated except Epithalamus ablated. Oviposition I normal. Re- caudal edge of preoptic nuclei dorsal to chiasma lease immediate. Oviposition II normal. Release and slight remnant of posterior pole on right side. immediate. Warning croak elicited. Swimming re- Oviposition I normal. Released after 1 hour. Eggs action to estrous female demonstrated. fertile. Oviposition II normal. No release in 4 MALE 65: Posterior poles of both cerebral hem- hours. Eggs fertile. Oviposition III normal. No ispheres ablated. Extensive lesion throughout release in 4 hours. Eggs fertile. Oviposition IV hippocampi and piriform areas. Anterior commis- normal. Oviposition V normal. No release in 5 sure and preoptic area intact. Swimming reaction hours. Warning croak elicited. No response to to estrous female demonstrated. estrous female observed. MALE 67: Epithalamus ablated. Extensive le- MALE 50: Forebrain completely ablated. Slight sion in dorsal part of dorsal thalamus. Emenentia damage to anterior edge of dorsal and ventral tha- thalami invaded. Cerebral hemispheres ablated lami. Release immediate. Warning croak elicited. from level of the anterior commissure to the pos- MALE 51: Lesion same as male 2. Warning terior poles. Sex call heard. Swimming reaction to croak elicited. Sex call heard. Swimming reaction estrous female demonstrated. to estrous female observed. MALE 68: Lesion same as male 8. Oviposition 120 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 I normal. Release delayed 4 minutes. Eggs not lease in 3 hours. Eggs fertile. Warning croak elic- fertile. Oviposition II normal. Release delayed 3 ited. Swimming response to estrous female ob- minutes. Eggs not fertile. Oviposition III normal. served. Release immediate. Eggs not fertile. Warning MALE 86: Hypothalamus ablated except nu- croak elicited. Swimming reaction to estrous fe- cleus suprachiasmaticus. Oviposition normal. No male demonstrated. release in 1 hour. Eggs fertile. No swimming re- MALE 70: Forebrain ablated except preoptic sponse to estrous female observed. area and ventral remnants of the corpora striata MALE 88: Lesion same as male 85. Oviposition and septal nuclei. Anterior commissure and re- I normal. No release after 1 hour. Oviposition II lated bed nuclei intact. Warning croak elicited. normal. No release after 3 hours. Eggs fertile. Sex call heard. Swimming reaction to estrous fe- Swimming response to estrous female demon- male demonstrated. strated. MALE 72: Lesion same as male 24. Swimming MALE 89: Lesion same as male 40. Warning reaction to estrous female not demonstrated. croak elicited. Swimming reaction to estrous fe- MALE 73: Forebrain ablated except slight rem- male demonstrated. nant of left posterior pole. Right habenular nuclei MALE 91: Lesion same as male 86. Swimming ablated and right emenentia thalami invaded. reaction to estrous female not demonstrated. Swimming reaction to estrous female not demon- MALE 92: Lesion same as male 8. Warning strated. croak elicited. Swimming reaction to estrous fe- MALE 74: Lesion same as male 16. Swimming male demonstrated. reaction to estrous female not demonstrated. MALE 93: Hypothalamus ablated except nu- MALE 75: Anterior third of cerebral hemi- cleus suprachiasmaticus. Nucleus ventralis tha- spheres ablated. Swimming reaction to estrous fe- lami pars externa invaded. Oviposition I normal. male not demonstrated. Oviposition II normal. Oviposition III normal. MALE 76: Forebrain ablated except caudal Oviposition IV normal. No release after 1 hour. remnants of preoptic nuclei dorsal to the chiasma. Eggs not fertile. Swimming response to estrous fe- Emenentia thalami, nuclei of Bellonci, habenular male demonstrated. nuclei, and anterior edges of dorsal and ventral MALE 94: Forebrain ablated. Epithalamus ab- thalamic nuclei extirpated. Swimming reaction to lated. Dorsal edge of dorsal thalamic nuclei extir- estrous female not demonstrated. pated. Anterior edge of ventral thalamus invaded. MALE 77: Forebrain ablated except caudal edge Warning croak elicited. Swimming reaction to of preoptic area. Emenentia thalami ablated. Ha- estrous female not demonstrated. benular nuclei invaded. Swimming reaction to MALE 95: Cerebral hemispheres ablated. Cau- estrous female not demonstrated. dal half of preoptic area intact. Anterior commis- MALE 78: Cerebral hemispheres ablated. Cau- sure and related bed nuclei intact. Warning croak dal two-thirds of preoptic area intact. Anterior elicited. Swimming reaction to estrous female not commissure and related bed nuclei intact. Swim- demonstrated. ming reaction to estrous female not demonstrated. MALE 96: Lesion same as male 40. Warning MALE 79: Lesion same as male 8. Warning croak elicited. Swimming reaction to estrous fe- croak elicited. Swimming reaction to estrous female not demonstrated. male noted. MALE 97: Lesion same as male 86. Oviposition MALE 80: Preoptic area completely ablated. I normal. Oviposition II normal. Released after 2 Anterior commissure and related bed nuclei hours. Warning croak elicited. Swimming reac- mostly removed. Slight damage to ventral edges tion to estrous female observed. of septal nuclei and corpora striata rostral to the MALE 98: Lesion same as male 32. Swimming preoptic area. Swimming reaction to estrous fe- reaction to estrous female not demonstrated. male not demonstrated. MALE 99: Lesion same as male 40. Oviposition MALE 82: Lesion same as male 32. Swimming normal. Release delayed i hour. reaction to estrous female not demonstrated. MALE 100: Dorsal thalamus, ventral thalamus, MALE 83: Lesion same as male 46. Swimming and epithalamus completely ablated. Extensive reaction to estrous female not demonstrated. injury to caudal third of forebrain. Slight inva- MALE 84: Lesion same as male 24. Swimming sion of hypothalamus. Warning croak elicited. reaction to estrous female not demonstrated. MALE 101: Tecta, inferior colliculi, ganglia MALE 85: Hypothalamus ablated except the isthmi, and cerebellum ablated. Slight invasion of suprachiasmatic nuclei and remnants of the pars caudal end of dorsal thalamus. Warning croak dorsalis. Oviposition I normal. Released after 1 could not be elicited. hour. Eggs fertile. Oviposition II normal. No re- MALE 103: Lesion same as male 46. Swimming lease in 4 hours. Oviposition III normal. No re- reaction to estrous female not demonstrated. 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 121 MALE 104: Lesion same as male 32. Preoptic ing croak elicited. Swimming reaction to estrous area intact. Anterior commissure and related bed female demonstrated. nuclei extirpated. Swimming reaction to estrous MALE 123: Lesion same as male 24. Oviposition female demonstrated. normal. Release immediate. Warning croak elic- MALE 105: Lesion same as male 95. Warning ited. croak elicited. Swimming reaction to estrous fe- MALE 125: Forebrain ablated except preoptic male demonstrated. area. Anterior commissure and related bed nuclei MALE 106: Forebrain, emenentia thalami, and ablated. Epithalamus ablated. Emenentia thalami nuclei of Bellonci completely ablated. Warning and nuclei of Bellonci invaded. Oviposition I nor- croak elicited. Swimming reaction to estrous fe- mal. Release immediate. Oviposition II normal. male not demonstrated. Release immediate. Eggs not fertile. Warning MALE 108: Forebrain ablated except caudal croak elicited. Sex call heard. Swimming reaction third of preoptic nuclei. Dorsal thalamus, ventral to estrous female demonstrated. thalamus, and epithalamus ablated. Anterior MALE 126: Lesion same as male 76. Oviposition edges of tecta slightly invaded. Warning croak I normal. Release delayed 2 hours. Oviposition II elicited. normal. Released in 15 minutes. Warning croak MALE 109: Lesion in dorsal thalamic nuclei. elicited. Pretectal nuclei and nuclei of posterior commis- MALE 127: Lesion same as male 24. Oviposition sure extensively damaged. Slight invasion of tecta I normal. No release in 1 hour. Oviposition II nor- and inferior colliculi. Warning croak elicited. Sex mal. Released in 1 hour. Eggs fertile. Warning call heard. croak elicited. Swimming response to estrous fe- MALE 112: Dorsal thalamus, ventral thalamus, male observed. and epithalamus ablated. Caudal third of fore- MALE 128: Forebrain completely ablated. Eme- brain extensively invaded. Warning croak elicited. nentia thalami and nuclei of Bellonci ablated. An- Slight invasion of anterior edge of hypothalamus. terior edges of dorsal and ventral thalamic nuclei Warning croak elicited. and rostral end of habenular nuclei damaged. Ovi- MALE 114: Epithalamus ablated. Dorsal and position I normal. No release in 1 hour. Eggs fer- ventral thalami ablated except caudal remnants. tile. Oviposition II normal. No release in 2 hours. Extensive invasion of posterior third of fore- Eggs fertile. Warning croak elicited. brain. Warning croak elicited. Swimming response MALE 133: Lesion same as male 76. Oviposition to estrous female observed. normal. Release immediate. Eggs fertile. MALE 115: Forebrain completely ablated. Eme- MALE 134: Cerebral hemispheres ablated ex- nentia thalami, anterior edges of dorsal and ven- cept caudal quarter of preoptic area which is tral thalami, nuclei of Bellonci, lateral geniculate slightly invaded. Emenentia thalami and nuclei of nuclei, and habenular nuclei ablated. Warning Bellonci invaded. Habenular nuclei ablated. Ovi- croak elicited. Sex call heard. Swimming reaction position normal. Release delayed j hour. to estrous female not demonstrated. MALE 135: Lesion same as male 46. Oviposition MALE 116: Epithalamus ablated. Dorsal and normal. Released after 1 hour. Warning croak ventral thalami largely ablated except at caudal elicited. end. Caudal third of forebrain extensively in- MALE 140: Forebrain, epithalamus, and eme- vaded. Slight damage to hypothalamus. Warn- nentia thalami ablated. Anterior edges of nuclei of ing croak elicited. Swimming response to estrous Bellonci, dorsal thalamic nuclei, and ventral tha- female observed. lamic nuclei invaded. Warning croak elicited. MALE 117: Lesion same as male 116. Warning Swimming reaction to estrous female observed. croak elicited. MALE 143: Forebrain ablated except caudal remnants of preoptic nuclei dorsal to chiasma. On MALE 118: Lesion same as male 114. Warning right side, the emenentia thalami, croak elicited. Swimming response to estrous fe- the nucleus of male observed. Bellonci, and the lateral geniculate nucleus were ablated. The right dorsal and ventral thalamic nu- MALE 119: Forebrain ablated except caudal clei were extensively invaded. Oviposition normal. remnants of the preoptic nuclei dorsal to chiasma. No release after 40 minutes. Eggs fertile. Warning Swimming reaction to estrous female demon- croak elicited. strated. MALE 155: Forebrain completely ablated. Eme- MALE 120: Lesion same as male 32. Swimming nentia thalami, anterior edges of dorsal and ven- reaction to estrous female not demonstrated. tral thalami, nuclei of Bellonci, and left habenular MALE 121: Forebrain ablated except preoptic nucleus extirpated. Swimming reaction to estrous nuclei dorsal to chiasma. Right nucleus of Bel- female not demonstrated. lonci and right emenentia thalami invaded. Warn- MALE 212: Extensive lesion in left tectum. Ovi- 122 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86

pim.d. ~~~~~~~~~~prn.sepoLd i

endofheprepti aea.Theleioni exeddaog h eta surfapce ftefrbanframs homm.1

caudally through the caudal end of the preoptic nucleus. The lesion extended about 90u caudal to this level. position normal. Release immediate. Eggs fertile. nuclei. Slight damage to ventral edges of septal Warning croak elicited. Sex call heard. nuclei and corpora striata. Oviposition normal. MALE 213 (FIG. 19): Preoptic area ablated ex- No release after 5 hours. Swimming reaction to cept caudal remnants of preoptic nuclei dorsal to estrous female demonstrated. chiasma. Ventral edges of septal nuclei and cor- MALE 223: Preoptic area ablated except caudal pora striata just anterior to the preoptic area in- remnant of preoptic nuclei dorsal to chiasma. De- vaded. Decussations of medial and lateral fore- cussations of medial and lateral forebrain bundles brain bundles and related bed nuclei invaded. and related bed nuclei extensively invaded. Slight Right amygdala injured. Oviposition normal. Re- damage to ventral edge of corpora striata, partic- lease delayed over 2 hours. Eggs fertile. ularly on the right side. Slight injury to ventral MALE 214: Tecta and inferior colliculi com- edge of medial and lateral septal nuclei. Slight in- pletely ablated. Slight damage to caudal end of vasion of anterior edge of thalamus on right side. thalamus. Warning croak could not be elicited. Ovipositon normal. Release delayed 1 hour. Eggs MALE 215: Preoptic nuclei completely ablated. fertile. 2 Nuclei suprachiasmatici hypothalami extensively MALE 233 (FIG. 20): Tecta ablated. Inferior damaged. Slight injury to decussations of medial colliculi ablated except remnants along ventral and lateral forebrain bundles and associated bed edges. Nuclei of the posterior commissure and

A B

;.OcoL oq. gong. isth cent gw - oq. Ln.It cent gr rL int n. it. -hyp. hp C D FIG. 20. Four transverse sections of the brain of operated male 233; X9. A. Through the caudal part of the thalamus. The lesion extended anteriorly along the dorsal surface of the diencephalon for about 300,u from this level. B. 600;& farther caudally through the anterior part of the tectum. C. 1 mm. farther caudally through the middle of the inferior colliculi. D. 345p caudally through-.a--**--the gangliatsr5.7_~~~ilZfisthmi. 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 123 pretectal nuclei ablated. Dorsal half of posterior anterior edge. Pretectal nuclei and nuclei of poste- portion of dorsal thalamic nuclei ablated. Dorsal rior commissure invaded. Oviposition normal. No half of central gray surrounding aqueduct exten- release in 7 hours. Eggs fertile. Warning croak sively injured. Oviposition normal. Release imme- could not be elicited. diate. Eggs fertile. Warning croak could not be MALE 313: Tecta completely ablated. Dorsal elicited. Sex call heard repeatedly. half of dorsal thalamus ablated. Inferior colliculi, MAL.E 241: Tecta, inferior colliculi, cerebellum, ganglia isthmi, and mesencephalic central gray pretectal nuclei, and nuclei of the posterior com- ablated. Lesion invaded tegmentum along mid- missure completely extirpated. Extensive invasion line at level of interpeduncular nucleus injuring of ganglia isthmi. Slight invasion of caudal edge of the latter. Oviposition abnormal. Release imme- dorsal thalamus. Oviposition normal. No release diate. Eggs not fertile. Warning croak could not in 5 hours. Warning croak elicited. be elicited.

8 A c FIG. 21. Three transverse sections through the brain of operated male 314; X9. A. Through the anterior part of the tectum. Lesion extended anteriorly from this level for about 450,u along the dorsal surface of midbrain. B. 390,u farther caudally through the middle of the tectum. C. 375,u farther caudally through the ganglia isthmi.

MALE 242: Transection at anterior edge of cere- MALE 314 (FIG. 21): Tecta ablated except lat- bellum. Warning croak could not be elicited. eral remnants at anterior end. Pretectal nuclei, MALE 301: Preoptic area ablated. Septal nuclei nuclei of the posterior commissure, and inferior mostly destroyed. Extensive lesion in corpora colliculi bilaterally ablated. Warning croak could striata. Anterior commissure and related bed nu- not be elicited. clei extirpated. Nuclei suprachiasmatici hypo- MALE 321: Tecta and inferior colliculi com- thalami invaded. Oviposition normal. Release pletely ablated. Caudal half of thalamus invaded. delayed 10 minutes. Warning croak could not be elicited. MALE 302: Preoptic area ablated except caudal MALE 322: Lesion same as male 24. Oviposition remnants of preoptic nuclei dorsal to the chiasma. normal. Warning croak elicited. Decussations of medial and lateral forebrain bun- MALE 324: Epithalamus ablated. Dorsal and dles partially interrupted. Septal nuclei invaded. ventral thalami ablated except near rostral and Oviposition normal. No release in 8 hours. Sex caudal ends. Caudal third of forebrain extensively call heard. invaded. Some damage to right tectum. Warning MALE 304: Cerebellum ablated. Caudal third croak elicited. Swimming response to estrous fe- of left tectum and caudal two-thirds of right tec- male observed. tum ablated. Warning croak elicited. MALE 331: Epithalamus ablated. Dorsal and MALE 311: Tecta completely ablated except ventral thalami ablated except caudal remnants. lateral remnant on right side. Inferior colliculi Caudal third of forebrain extensively invaded. extensively invaded. Posterior part of dorsal thal- Anterior part of tecta damaged. Warning croak amus mostly ablated. Tegmentum invaded on elicited. Swimming response to estrous female left side only at level of interpeduncular nucleus. demonstrated. Trochlear and oculomotor nuclei ablated. Nu- MALE 333: Caudal half of tectum ablated. Cau- cleus opticus tegmenti and nucleus lateralis pro- dal end of inferior colliculi invaded. Cerebeltum fundi ablated on left side. Pretectal nuclei and nu- ablated. Oviposition normal. Release delayed 1 clei of the posterior commissure ablated. Oviposi- hour. Eggs fertile. Warning croak elicited. tion normal. Release delayed 5 hours. Eggs fer- MALE 341: Forebrain completely ablated. Epi- tile. Warning croak could not be elicited. thalamus ablated. Dorsal and ventral thalami MALE 312: Tectum ablated except lateral edges ablated except caudal remnants. Warning croak at anterior end. Inferior colliculi ablated except elicited. 124 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86

B c FIG. 22. Three transverse sections through the brain of operated male 414; X9. A. Through the middle of the tectum. Intact brain tissue extended about 300,u anterior to this level. B. 540,u farther caudally through the caudal part of the tectum. C. 195,u farther caudally through the ganglia isthmi.

MALE 342: Transection a little rostral to the MALE 413: Forebrain completely ablated. Ep- caudal end of the oculomotor nuclei. Tecta thalamus ablated. Dorsal and ventral thalamus ablated except caudal lateral edges. Oviposition ablated except caudal edges of dorsal and ventral normal. thalamic nuclei. Pretectal nuclei and nuclei of the MALE 343: Hypothalamus ablated except rem- posterior commissure intact. Oviposition normal. nants of nuclei suprachiasmatici. Slight invasion Eggs fertile. Warning croak elicited. of ventral thalamic nuclei pars externa and the MALE 414 (FIG. 22): Transection just anterior preoptic nuclei. Oviposition normal. No release to caudal end of oculomotor nuclei. Tecta extir- after 5 hours. Eggs fertile. pated except caudal remnant on right side. Left MALE 344: Hypothalamus completely ablated. inferior colliculus ablated. Right inferior col- Slight invasion of ventral edges of preoptic nuclei. liculus damaged. Oviposition normal. Release im- Optic chiasma mostly ablated. Oviposition nor- mediate. Eggs fertile. Warning croak could not be mal. No release in 1 hour. Eggs fertile. Warning elicited. croak elicited. MALE 422: Forebrain completely ablated. Dor- MALE 402: Forebrain completely ablated. Epi- sal and ventral thalami ablated except at caudal thalamus ablated. Dorsal and ventral thalami end. Epithalamus removed. Warning croak pres- ablated except caudal remnants. Extensive lesion ent. in roof of tecta and slight invasion of caudal end MALE 424: Transection at anterior end of teg- of inferior colliculi. Warning croak could not be mentum. Tecta and inferior colliculi completely elicited. ablated. Small lesion extended caudally near mid- MALE 403: Lesion same as male 85. Oviposition line of tegmentum to level of trochlear nucleus. normal. Release immediate. Eggs fertile. Warning Oviposition abnormal. Eggs fertile. Warning croak elicited. Sex call heard. croak could not be elicited. MALE 411: Transection at caudal level of oculo- MALE 431: Transection at caudal end of cere- motor nuclei. Anterior half of tectum ablated. An- bellum. Warning croak could not be elicited. terior edge of inferior colliculus invaded on left MALE 433 (FIG. 23): Transection at level just side. Tegmentum ablated to caudal end of oculo- anterior to oculomotor nucleus. Tecta ablated ex- motor nuclei. Oviposition abnormal. Release im- cept lateral remnants. Anterior edge of inferior mediate. Eggs fertile. Warning croak elicited. colliculi damaged, rest intact. Oviposition normal. MALE 412: Forebrain completely ablated. Ros- Eggs not fertile. Warning croak elicited. tral half of dorsal and ventral thalami ablated. Le- MALE 441: Complete transection through gan- sion extended caudally into dorsal thalamic nuclei. glia isthmi. Warning croak could not be elicited. Epithalamus extirpated. Warning croak elicited. MALE 443: Transection at caudal end of inter-

A B C FIG. 23. Three transverse sections through the brain of operated male 433; X9. A. Through middle of tectum. Intact brain tissue extended about 225,u anterior to this level. B. 290,u farther caudally through the posterior part of the tectum. C. 260,u farther caudally through the ganglia isthmi. 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 125 peduncular nucleus. Tecta, inferior colliculi, and MALE 702: Deep midline lesion along entire ganglia isthmi completely ablated. Oviposition rostro-caudal extent of tegmentum ablating the abnormal. Eggs not fertile. Warning croak could nucleus interpeduncularis. Pars ventralis hypo- not be elicited. thalami ablated except the nuclei suprachiasma- MALE 521: Transection at caudal end of oculo- tici. Pars dorsalis hypothalami injured. Oviposi- motor nuclei. Tecta and inferior colliculi com- tion abnormal. Eggs not fertile. pletely ablated. Injury to tegmentum extended MALE 704: Hypothalamus ablated except nu- caudally to trochlear nuclei. Oviposition abnor- clei suprachiasmatici. Deep midline lesion extend- mal. Release immediate. Eggs not fertile. Warning ing from the anterior to the posterior end of the croak could not be elicited. tegmentum and invading the rostral part of the MALE 523: Transection through interpeduncu- medulla oblongata. Oculomotor nuclei, trochlear lar nucleus. Tecta and inferior colliculi ablated. nuclei, nuclei optici tegmenti, and interpedun- Oviposition abnormal. cular nucleus invaded. Warning croak could not be MALE 531: Transection just caudal to cere- elicited. bellum. Warning croak could not be elicited. MALE 711: Hypothalamus ablated. Anterior MALE 532: Transection at caudal end of cere- tegmentum ablated to level of trochlear nuclei. bellum. Oviposition abnormal. Released in 3 min- Right inferior colliculus mostly destroyed; left in- utes. Eggs not fertile. Warning croak could not be ferior colliculus intact. Ventral thalamic nuclei elicited. invaded on right side. Slight injury to right pre- MALE 542: Shallow ablation of entire rostro- optic nucleus. Warning croak could not be elicited. caudal extent of tegmentum. Lesion deeper at MALE 712: Transection just anterior to cere- caudal end to include interpeduncular nucleus and bellum. Oviposition abnormal. Released in 4 min- right ganglion isthmi. Pars ventralis hypothalami utes. Eggs not fertile. Warning croak could not be mostly ablated on right side and invaded on left elicited. side. Lateral edge of thalamus injured on right MALE 713: Large midline lesion along entire side. Oviposition abnormal. No release for 45 min- rostro-caudal extent of tegmentum ablating the utes when male died. Eggs not fertile. nucleus interpeduncularis, the oculomotor and

A B c FIG. 24. Three transverse sections through the brain of operated male 603; X9. A. Through the middle of the tegmentum. Lesion extended along the ventral surface of the tegmentum for about 300,u anterior to this level. B. 4951U farther caudally through the posterior part of the tegmentum. C. 165,u farther caudally through the posterior part of the tegmentum. MALE 603 (FIG. 24): Lesion in tegmentum trochlear nuclei, the nuclei profundi laterale, the along midline starting at caudal end of oculo- nuclei optici tegmenti, and the ventral half of the motor nuclei and extending to medulla. Left mesencephalic central gray. Hypothalamus com- trochlear nucleus ablated; right mostly intact. In- pletely ablated except remnants of suprachiasmat- terpeduncular nucleus ablated. At caudal end of ic nuclei. Both ganglia isthmi invaded. Oviposi- midbrain, the central gray surrounding the aque- tion abnormal. Release immediate. duct was invaded. Oviposition abnormal. Re- MALE 714: Broad deep extirpation along entire lease immediate. Eggs not fertile. Oviposition II rostro-caudal extent of tegmentum ablating the abnormal. Release immediate. Eggs not fertile. interpeduncular nucleus, the oculomotor and Warning croak elicited. trochlear nuclei, the nuclei profundi laterale, the MALE 604: Pars ventralis hypothalami ablated nuclei optici tegmenti, and the ventral half of except suprachiasmatic nuclei. A shallow mid- the mesencephalic central gray. Hypothalamus line tegmental lesion extended caudally to rostral ablated except remnants of suprachiasmatic nu- level of interpeduncular nucleus. Oviposition nor- clei. Caudal two-thirds of tecta ablated except mal. Release immediate. Eggs not fertile. Warning lateral edges. Inferior colliculi ablated except ven- croak elicited. tral remnants. Cerebellum ablated. Oviposition 126 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 abnormal. Release delayed 25 minutes. Eggs fer- MALE 743: Epithalamus ablated. Dorsal and tile. Warning croak could not be elicited. ventral thalami ablated except caudal remnants. MALE 721: Hypothalamus extirpated except Left cerebral hemisphere largely ablated. Caudal nuclei suprachiasmatici. Tegmentum ablated ex- third of right hemisphere extensively invaded. cept lateral edges. Inferior colliculi extensively Warning croak elicited. invaded with some damage to the caudal part of MALE 801: Extensive invasion of dorsal and the tecta. Warning croak could not be elicited. ventral thalamic nuclei and the habenular nuclei. MALE 722: Transection at the anterior end of Slight invasion of the posterior poles of the hemi- the oculomotor nuclei. Tecta and inferior colliculi spheres and the nuclei suprachiasmatici hypo- extensively damaged. Warning croak could not be thalami. Oviposition normal. No release after 15 elicited. hours. Eggs fertile. Warning croak elicited. Sex MALE 723: Transection near caudal end of call heard. cerebellum. Warning croak could not be elicited. MALE 802: Dorsal and ventral thalami mostly MALE 724: Broad deep lesion along entire ablated, except caudal edges and lateral edge on rostro-caudal extent of tegmentum ablating the right side. Epithalamus removed. Posterior pole nucleus interpeduncularis, the oculomotor and of left cerebral hemisphere destroyed to level of trochlear nuclei, the nuclei profundi laterale, the anterior commissure. Oviposition I normal. Ovi- nuclei optici tegmenti, and the ventral edges of position II normal. Release delayed 2 hours. Eggs the mesencephalic central gray. Hypothalamus fertile. ablated except suprachiasmatic nucleus. Oviposi- MALE 805: Epithalamus ablated. Dorsal and tion abnormal. Release immediate. Eggs not fer- ventral thalamri ablated, except caudal and ven- tile. Warning croak elicited. tral edges. Extensive injury to posterior third of MALE 731: Transection through anterior end of forebrain. Warning croak elicited. tegmentum. Tecta ablated except dorsal and lat- MALE 813: Hippocampi and piriform areas eral remnants. Inferior colliculi ablated except ablated except ventral remnants. Oviposition nor- caudal remnants. Tegmentum invaded to level of mal. Release immediate. Warning croak elicited. trochlear nucleus. Oviposition I abnormal. Re- Sex call heard. Swimming reaction to estrous fe- lease delayed 11 minutes. Eggs not fertile. Ovipo- male observed. sition II abnormal. Release delayed 5 minutes. MALE 815: Dorsal thalamus destroyed except Eggs fertile. Warning croak could not be elicited. remnants along the ventral edge. Slight invasion MALE 733: Anterior half of tegmentum mostly of ventral thalamus. Epithalamus ablated. Exten- ablated. Lesion extended caudally to interpedun- sive invasion of the primordia hippocampi. Ovipo- cular nucleus which was slightly damaged. Hypo- sition normal. Release delayed 4 minutes. Eggs thalamus completely ablated. Inferior colliculi ex- fertile. Warning croak elicited. Sex call heard. tensively injured. Ventral thalamus on left side MALE 816: Epithalamus ablated. Small lesion extensively injured and lesion extended to dorsal in primordia hippocampi. Warning croak elicited. thalamus. Oviposition abnormal. Release imme- Sex call heard. diate. Warning croak could not be elicited. MALE 822: Epithalamus ablated. Dorsal edge MALE 734: Hypothalamus ablated. Tegmen- of dorsal thalamic nuclei invaded. Warning croak tum extirpated to middle level of oculomotor nu- elicited. Sex call heard. cleus. Inferior colliculi and ventral edge of dorsal MALE 823: Epithalamus extirpated. Extensive thalamus invaded. Preoptic area and optic chi- lesion in dorsal half of dorsal thalamus. Oviposi- asma destroyed. Lesion extended into right cere- tion normal. Release immediate. Eggs not fertile. bral hemisphere at level of anterior commissure, MALE 831: Hypothalamus ablated except nu- particularly the right primordium hippocampus. clei suprachiasmatici. Anterior third of tegmen- Oviposition normal. No release in 3 hours. Eggs tum mostly ablated. Warning croak elicited. not fertile. Swimming reaction to estrous female observed. MALE 741: Forebrain, dorsal thalamus, ventral MALE 832: Hypothalamus ablated except rem- thalamus, and epithalamus ablated. Anterior ends nants of suprachiasmatic nuclei. Ventral thalamic of hypothalamus and tecta invaded. Warning nuclei, pars externa invaded. Rostral end of teg- croak elicited. mentum ablated to anterior level of oculomotor MALE 742: Posterior poles of cerebral hemi- nuclei. Nu'cleus opticus tegmenti ablated. Ovipo- spheres ablated from level of interventricular fo- sition normal. Release delayed 4 hours. Eggs fer- ramen. Anterior commissure and related bed nu- tile. Warning croak elicited. clei ablated. Preoptic area intact. Anterior end of MALE 841: Pars ventralis hypothalami mostly epithalamus, dorsal thalamus, and ventral thal- ablated except the suprachiasmatic nuclei. Ovi- amus invaded. Warning croak elicited. Swimming position normal. Release immediate. Eggs fertile. reaction to estrous female demonstrated. MALE 842: Large lesion in rostral half of pars 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 127 ventralis hypothalami. Oviposition normal. Re- MALE 911: Forebrain and epithalamus com- lease immediate. Eggs fertile. Warning croak pletely ablated. Dorsal thalamus, ventral thal- elicited. amus, and hypothalamus ablated except at caudal MALE 844: Large lesion in caudal half of pars end. Warning croak elicited. ventralis hypothalami. Oviposition normal. Re- MALE 915: Extensive bilateral lesions in hippo- lease immediate. Eggs fertile. Warning croak campi and piriform areas. Anterior commissure elicited. and preoptic area intact. Left habenular nuclei MALE 845: Lesion same as male 86. Oviposition ablated, and edges of left dorsal and ventral thal- normal. Release immediate. Eggs not fertile. ami invaded. Warning croak elicited. Swimming Warning croak elicited. reaction to estrous female demonstrated.

w-Prim hip.

n pripx pir. corp.strLLb.nc.L b. n. dec. L L b. s:47 dec.Lf.b. olny. n.preop. pen. n. preop. pen. corp. str. . .n.preoOP*.nLL fb. A tL preop.m B C FIG. 25. Three transverse sections through the brain of operated male 918; X9. A. Through the anterior end of the preoptic area. Lesion extended about 375,g anterior to this level. B. 90,u farther caudally through the middle of the preoptic area. C. 135ju farther caudally through the posterior part of the preoptic area. The lesion extended about 45, caudad from this level.

MALE 901: Midsagittal cut through midbrain. MALE 918 (FIG. 25): Left half of preoptic area At anterior end, incision extended from third ven- largely extirpated. Anterior commissure and re- tricle to dorsal surface cutting posterior and tectal lated bed nuclei extensively invaded. Oviposition commissures. At level of inferior colliculi cut ex- I normal. Oviposition II normal. Release delayed tended into the aqueduct, and from interpedun- 10 minutes. Eggs not fertile. Oviposition III nor- cular nucleus to medulla cut extended from dorsal mal. Release immediate. Eggs not fertile. Oviposi- to ventral surfaces. Warning croak elicited. tion IV normal. Eggs not fertile. Oviposition V MALE 903: The following areas were completely normal. No release in 15 minutes. Eggs fertile. ablated: tecta, inferior colliculi, cerebellum, gan- Oviposition VI normal. Released immediately. glia isthmi, nucleus pretectalis, and nucleus of the Warning croak elicited. Swimming reaction to posterior commissure. The caudal portions of the estrous female demonstrated. nuclei dorsalis thalami pars interna and externa MALE 920: Lesion same as male 11. Oviposition were ablated, and the central gray around the I normal. Oviposition II normal. No release in 5 aqueduct was severely damaged, particularly the hours. Eggs not fertile. Warning croak elicited. dorsal half. Oviposition normal. Release imme- Swimming reaction to estrous female demon- diate. Eggs fertile. Warning croak could not be strated. elicited. MALE 921: Anterior third of preoptic area MALE 906: Pars ventralis hypothalami ablated ablated. Slight invasion of ventral edges of septal except the nuclei suprachiasmatici. Some injury nuclei and corpora striata. Anterior commissure to ventral edge of the pars dorsalis hypothalami. intact. Oviposition I normal. No release in 5 hours. Oviposition I normal. Release delayed j hour. Eggs not fertile. Oviposition II normal. No release Eggs fertile. Oviposition II normal. Release imme- in 4 hours. Eggs not fertile. Oviposition III nor- diate. Warning croak elicited. Sex call heard. mal. No release in 4 hours. Oviposition IV normal. Swimming response to estrous female observed. No release in 4 hours. Oviposition V normal. No MALE 907: Lesion same as male 841. Oviposi- release in 3 hours. Eggs fertile. Swimming reaction normal. Release immediate. Eggs fertile. tion to estrous female noted. MALE 910: Bilateral lesion along entire length MALE 922: Lesion same as male 11. Oviposition of hippocampi slightly injuring the piriform areas. I normal. Release delayed 41 minutes. Eggs fer- Oviposition normal. Release immediate. Warning tile. Oviposition II normal. Release delayed 9 min- croak elicited. Swimming reaction to estrous fe- utes. Eggs not fertile. Swimming reaction to est- male demonstrated. rous female demonstrated. Sex call heard. 128 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 MALE 923: Lesion same as male 62. Oviposi- septum on right side. Anterior commissure and re- tion normal. Release delayed over 2 hours. Eggs lated bed nuclei invaded. Sex call heard. Swim- not fertile. Warning croak elicited. Sex call heard. ming response to estrous female demonstrated. Swimming reaction to estrous female demon- MALE 939: Cerebral hemispheres ablated. Cau- strated. dal two-thirds of preoptic area intact. Anterior MALE 924: Lesion same as male 85. Oviposition commissure and related bed nuclei mostly inter- I normal. Release immediate. Eggs not fertile. rupted. Epithalamus ablated. Emenentia thalami Oviposition II normal. Release immediate. Eggs and nuclei of Bellonci invaded. Warning croak not fertile. Warning croak elicited. Sex call heard. elicited. Swimming reaction to estrous female Swimming reaction to estrous female noted. demonstrated.

post. pole n.hob. tect. N n. dor.thaL n.doc thai. n.vent. thai In?. vent. thaL sett. A,d,rhpsWr nopt.Bt A dor. hyp B

- :e~~~~~~~#ct. tect. -int coL

-centgr. cet r

D C FIG. 26. Four transverse sections through the brain of operated male 928; X9. A. Through the anterior part of the hypothalamus. Lesion extended about lO5,u anterior to this level. B. 495u farther caudally through the posterior end of the hypothalamus. C. 495,u farther caudally through the middle of the tegmentum. D. 480, farther caudally through the posterior part of the tegmentum.

MALE 928 (FIG. 26): Hypothalamus ablated ex- MALE 941: Hypothalamus ablated. Optic chi- cept nuclei suprachiasmatici. Midventral lesion asma destroyed. Slight invasion of caudal end of along entire rostro-caudal extent of tegmentum. preoptic nuclei. Oviposition I normal. Release Nucleus interpeduncularis ablated and nuclei delayed 8 minutes. Eggs not fertile. Oviposition optici tegmenti damaged. At level of cerebellum, II normal. Eggs not fertile. Oviposition III nor- lesion extended dorsally and damaged central gray mal. No release in 3 hours. Sex call heard. surrounding the aqueduct. Warning croak elicited. MALE 942: Rostral quarter of cerebral hemi- MALE 929: Extensive lesion in primordia hippo- spheres extirpated. Swimming reaction to estrous campi at level of interventricular foramen. On female demonstrated. left side the piriform area was invaded. Swimming MALE 945: Hypothalamus ablated except rem- reaction to estrous female demonstrated. nants of nuclei suprachiasmatici. Slight invasion MALE 930: Caudal two-thirds of pars ventralis of anterior edge of tegmentum. Oviposition nor- hypothalami ablated. Slight invasion of pars dor- mal. No release in 4 hours. Warning croak elic- salis hypothalami. Oviposition I normal. Release ited. immediate. Eggs not fertile. Oviposition II nor- MALE 946: Pars ventralis hypothalami ablated mal. Release immediate. Eggs not fertile. Sex call except suprachiasmatic nuclei. Pars dorsalis hypo- heard. Swimming reaction to estrous female dem- thalami intact. Oviposition normal. Warning onstrated. croak elicited. Sex call heard. Swimming reaction MALE 936: Left cerebral hemisphere ablated. to estrous female demonstrated. Extensive injury to primordium hippocampus and DISCUSSION IN RECENT YEARS the once popular concept of croak which functions efficiently without the "strict localization of function" within the participation of the forebrain, diencephalon, brain and spinal cord has been modified by cerebellum, and remaining midbrain areas most neurologists and psychologists. Much (superior colliculus and tegmentum) not in- more importance is now attributed to the cluded in this system. While this apparatus functional interrelationships of the various appears to be relatively independent of large neural systems (Papez, 1937; Bard, 1939) and areas of the brain, it is nevertheless conceiv- to the generalized autogenous activity and able that these regions do exert a slight reg- plasticity of the masses of central nervous ulatory influence on the warning croak as tissue, particularly the mammalian cerebral suggested by the work of Goltz (1869), Bech- cortex (Lashley, 1930, 1942). terew (1884), and Blankenagel (1931). Nevertheless, the precise definition of ana- Glass and Rugh (1944) have demonstrated tomical and physiological centers and sys- a sharp decrease in the amount of interstitial tems still remains a major tool in the hands tissue of the testes of Rana pipiens during the of the neurological investigator (Bard, 1939), summer months, and this in turn probably providing one constantly bears in mind that results in a reduced output of testicular hor- these localized areas and systems do not mone, although there is still some question as function independently in the intact animal; to the exact origin of this secretion. It has that the discrete activity hypothesized for a previously been noted that it is more difficult given region might be superimposed upon a to elicit the warning croak during the summer more general function of the same nervous months after the breeding season (Noble and tissue; and that, with the destruction of a Aronson, 1942), and hence this reduced vo- given region, the remaining parts of the brain cality may be correlated with a low produc- might reorganize some of the activity of the tion of testis hormone. If we accept the prev- damaged area. While these generalizations alent hypothesis that the gonadal hormones were developed mainly from mammalian sensitize certain central nervous mechanisms brain studies, there seems little reason to (Lashley, 1938) and reduce the thresholds of doubt that they apply to the lower verte- the motor circuits mediating or facilitating brates as well. sexual responses (Beach, 1942), it must then be concluded that the testicular hormone WARNING CROAK acts either upon the spinal cord, medulla ob- In the present investigation, the warning longata, caudal tegmentum, or inferior collic- croak mechanism appears to be the least com- ulus for the facilitation of the warning croak. plex and most easily analyzed. Tactile stim- An alternative explanation of the in- ulation of the back of the male is the primary creased difficulty of eliciting the warning stimulus which elicits the warning vocaliza- croak after the breeding season cannot be ex- tion (Noble and Aronson, 1942). cluded. It has been known for many years The sensory nerves to the skin of the back that after the spawning period, males of carry the tactile impulses to the spinal cord, many species of Anura undergo pronounced where they are relayed via the spino-tectal somatic changes. The most striking of the ex- tracts to the inferior colliculi. This latter re- ternal changes in Rana pipiens are the region appears to be. a center of sensori-motor gressions of the thumb pad and the brachial correlation which projects upon the motor and antibrachial musculatures associated centers in the medulla oblongata and spinal with the clasp reflex. Glass and Rugh (1944) cord by means of the tecto-bulbar and tecto- cite evidence showing that the secondary sex spinal tracts. Motor nerves from the medulla characters of Anura are controlled by gon- and spinal cord complete the circuit by carry- adal secretions, although the secretions of the ing the impulses to the buccal, hyoid, and ab- anterior pituitary gland may stimulate these dominal muscular complex. This circuit con- sex characters directly. Blair (in MS) has stitutes the basic mechanism of the warning shown that in juvenile male and female Bufo 129 130 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 fowleri the size of the laryngeal vocal appara- clasping would result. We are more inclined tus is strongly influenced by mammalian sex to agree with Baglioni (1913) who noted that hormones, particularly testosterone propio- the clasping behavior after midbrain injury is nate. It is conceivable that in Rana pipiens qualitatively different from the sexual clasp the waning of the warning croak response af- of the intact animal. Hence it is better to con- ter the breeding season is due in part to a re- sider the midbrain mechanism as a modifier gression of the laryngeal vocal apparatus. rather than an inhibitor of the spinal clasp reflex. SEX CALL Starting with extensive thalamic invasions The stimuli which call forth the sex croak and transections, we noted mild changes in are not well known, nor have we been able to the clasping behavior. As our invasions and define clearly the central nervous mecha- transections were placed farther and farther nisms responsible for this behavior. As for the caudally, the clasp became modified to a stimuli, it can be said that the voice of one greater and greater extent with the greatest calling male appears to stimulate other males modification occurring after transections to call, and if the experimenter imitates the through the medulla. sex call, the frog will sometimes give the re- In view of these observations, together sponse. Males often call as they swim after a with the fact that no specific loci for the mod- female, and the sex call and warning croak ification of the clasp were located, and con- are sometimes combined into what we have sidering that previous investigators had pos- termed the sex-warning croak (Noble and tulated various inhibitory centers in the dien- Aronson, 1942). Thus, optic and auditory cephalon, midbrain, cerebellum, and me- stimuli appear to arouse the sex call, and dulla, it is probably better to consider the other sensory stimuli may also be effective total structure of these regions as normally (Noble, 1931). contributing to the modification or regula- With this meager information we can out- tion of the spinal clasp reflex. line the sex call mechanism only in a very tentative fashion. Optic impulses to the tec- SPAWNING MOVEMENTS tum are relayed to the inferior colliculi, as are In our previous communication (Noble and auditory impulses from the cochlear nuclei Aronson, 1942) it was hypothesized that the in the medulla oblongata (nucleus dorsalis stimuli for the male's ejaculatory responses magnocellularis). Since in one of our operates derived from the oviposition movements of (male 233) the sex call was heard following the female, and that these stimuli impinged ablation of the tectum and inferior colliculi, upon the sensory receptors in the skin of the the sex call mechanism probably includes ventral pectoral region and ventral surfaces other midbrain areas, possibly the ganglion of the forelimbs. Sensory nerves from the re- isthmi, as we have already suggested. This ceptors convey impulses to the spinal cord region would then correlate the optic and whence they possibly are transmitted to the auditory impulses with the other sensory tegmentum by the component of the spino- stimuli which arouse the sex call, and would tectal tract (Papez, 1929) which terminates project on the lower motor centers. in this region. Herrick (1936) notes that in the motor teg- CLASP REFLEX mentum many of the most fundamental pat- Our observations on the effects of brain in- terns of behavior are organized. In Ambly- jury on the clasp reflex confirm the findings stoma, according to Herrick, the tegmentum of many previous investigators (Tarchanoff, "dreceives no sensory fibers directly from the 1887; Albertoni, 1887; Schrader, 1887; Stei- periphery except the nervus terminalis and nach, 1910; Busquet, 1910, 1910a), indicating the basal optic tract (tractus opticus accesso- that midbrain lesions affect the clasp reflex. rius posterior), most of its excitations coming Most of these authors hypothesized clasp in- from the centers of adjustment-cerebral hibitory centers located in the diencephalon, hemispheres, all parts of the diencephalon, midbrain, cerebellum, and medulla oblongata, tectum mesencephali, cerebellum, and the since with the removal of these areas, chronic sensory field of the medulla oblongata." 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 131 If Herrick's analysis of the tegmentum of tory response, thus accounting for the failure Amblystoma can be applied to Rana, it would of many of the males with such brain injury appear that the sensory excitations for the to release the female when the spawning ter- ejaculatory movements must come from the minates. sensory field of the medulla oblongata, since From table 5 it is seen that, following ex- the forebrain, diencephalon, tecta, inferior tensive hypothalamic and preoptic invasion, colliculi, and cerebellum may be removed in a few males still released. These exceptional their entirety without any noticeable dis- cases can be accounted for by assuming that turbances in this behavior. the sum of the stimuli received from the It is of interest to recall that Spallanzani other three factors causing a male to release (1786) reported normal spawnings of decapi- was greater than the necessary minimum. Re- tated males. However, it is not clear whether duction in girth and movement of the female Spallanzani actually witnessed the oviposi- seemed particularly important in these cases, tions, or whether he judged their normality and some males were actually seen to slide by the resulting embryos. Since one of our off the thin, actively moving females. males with a large tegmental lesion fertilized some eggs without showing any spawning or SWIMMING RESPONSE ejaculatory motions during an oviposition The swimming reaction of the sexually ac- with a normal female, it appears that some tive male towards the estrous female is pri- sperm may be discharged without the cus- marily a visually directed response (Noble tomary movements that accompany sperm and Aronson, 1942). Since some completely emission. decerebrate males exhibit this behavior, the forebrain cannot be considered a basic link in RELEASE the neural mechanisms responsible for this In our study of the normal behavior of behavior. Moreover, a few observations Rana pipiens, we postulated on the basis of (males 54, 114, 116, 118, 324, 331) indicate various bits of experimental evidence that that the response can sometimes be elicited the release of the female by the male at the after extensive diencephalic injury. It is not termination of the oviposition was due to a until the midbrain is destroyed that the re- complex of factors which included (1) the sponse is completely lost. Thus we should ejaculation of the male, (2) the reduction in consider the swimming response to the es- girth of the female, (3) the cessation of the trous female as being integrated primarily by female's oviposition movements, and (4) the the midbrain. movement of the female from the egg-laying The role of the forebrain in the mediation posture. It is believed that if the sum of the of the swimming response appears to be that sensory stimuli resulting from these actions of a facilitator or regulator. In this sense, the surpasses a certain minimum, release will oc- part played by the forebrain is comparable to cur. that of the cerebral cortex in mammals, where In mammals the genital organs are inner- the cortex is held to facilitate or control the vated in part by the autonomic nervous sys- "'ease of arousal of the copulatory pattern tem (Stone, 1923; Semans and Langworthy, which is mediated by the lower centers of the 1938), and the ejaculation is considered by brain stem and spinal cord" (Beach, 1940, some to include an autonomic discharge. In 1942). This interpretation of the function of Anura the genital organs are similarly inner- the mammalian cerebral cortex in relation to vated (Gaupp, 1899), and an autonomic reg- mating behavior agrees in part with Herrick's ulation of the ejaculatory response can be conception of the function of the cerebral hypothesized. The hypothalamus has long hemispheres in Amphibia. He states that in been recognized as an autonomic center for Amphibia "The cerebral hemispheres regu- the control of visceral responses, and it now late all diencephalic and mesencephalic func- appears likely that invasions of the hypo- tions, with a strong preponderance of olfac- thalamus and its rostral extension, the pre- tory influence. Inhibition, conditioning of re- optic area, result in a disturbance of the auto- flexes, an intrinsic activity which expresses nomic discharge associated with the ejacula- itself as so-called spontaneity, and a general 132 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 facilitation of lower functions are character- forebrain deprivation. While Blankenagel istic expressions of the activity of the cere- (1931) postulated two discrete centers in the bral hemispheres, and these are all repre- caudo-ventral part of the forebrain, one for sented at a low level of efficiency in the am- the mediation of feeding reactions and the phibian brain" (Herrick, 1933a).1 other for the swimming reaction to the fe- A second function of the forebrain, namely, male, our observations, agreeing with those the correlation of the various sensory im- of Diebschlag (1934), suggest that the hypo- pulses relayed from the dorsal thalamus, is thalamic-preoptic-septo-hippocampal mech- weakly developed in Amphibia, as reflected anism outlined above regulates all mass in the sparsity of thalamic radiations, and the movements requiring extensive sensori-motor presence of any correlative activity did not integration. In the frog these mass move- manifest itself in the foregoing experiments. ments are particularly involved in the re- The medial wall of the amphibian cerebral actions to food, response to a clasp object, hemisphere (hippocampus and septum), the and by general activity. preoptic area, and hypothalamus form an in- It is rather difficult to harmonize our re- tegrated system (Herrick, 1933). This system sults with the findings of those authors who is elaborated in higher vertebrates and hu- found no loss of "spontaneity" following fore- mans, and here it is believed to regulate the brain extirpation (Desmoulin, 1825; Schra- "conscious" or emotive state (Papez, 1937, der, 1887; Burnett, 1912). Schrader attempts 1937a, 1939). It seems probable that in Rana to explain this discrepancy by assuming that pipiens this system is the one which is in- other investigators inadvertently damaged volved in the facilitation of the swimming re- the diencephalon while removing the fore- action of the male towards the clasp object. brain, and we could likewise assume that Our findings suggest that as far as this gen- Schrader and Burnett left the preoptic area eralized facilitative function is concerned, intact. However, since none of the previous the medial wall of the hemisphere and the investigators included detailed descriptions preoptic area are not functionally discrete; of the lesions which they inflicted, such pos- for as long as either of these regions remains, tulations are fruitless. the response is readily exhibited, but if both There are other explanations which might are removed the response occurs only rarely. be advanced to account for these contradic- Although our data on this point are incom- tory findings. We have found that forebrain plete, they can be interpreted as indicating extirpation and extensive diencephalic injury that this facilitative function of the forebrain neither alter nor abolish the swimming re- can be maintained by a relatively small sponse; these operations merely reduce the amount of forebrain tissue which remains in frequency with which this behavior is dis- contact with the diencephalon. The fact that played. Hence the discrepancies noted above removal of most of the hypothalamus does might be due to a failure to test carefully a not markedly reduce the swimming response sufficient number of operated animals. Fi- seems to indicate that the system is still more nally, some degree of recovery of function diffuse than outlined above. can be expected after every injury to the cen- As already noted in the review of the litera- tral nervous system (Lashley, 1938a). The ture a number of authors have recognized a majority of studies have dealt with more facilitative function of the forebrain by re- or less immediate postoperative changes, cording the loss of spontaneity subsequent to whereas Schrader first tested his operated frogs aftet allowing them to hibernate over 1 A recent experiment by Detwiler (1944, Proc. Soc. Exp. Biol. Med., vol. 56, pp. 195-196) is of interest in the winter. this connection. He found that the lateral line system Males castrated prior to the breeding sea- alone was sufficient to elicit feeding reactions in Am- son do not exhibit the swimming response blystoma larvae whose eyes and nasal organs had been towards the estrous female (Schrader, 1887), removed. While this activity was carried.out in a nor- while in the intact animal this behavior is mal integrated manner in animals that also lacked the forebrain, feeding was reduced in both amount and vigor enhanced by anterior pituitary injections when compared to those larvae with similar sensory (Rugh, 1935a). The effectiveness of the pitu- deprivations but having intact cerebral hemispheres. itary treatment is believed to be due to in- 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA -13.3 creased hormone output by the testes result- These six phases of the male frog's sexual ing from gonadotropic effects of the pitui- behavior are discrete to the extent that each tary substance. In other words, male hor- one can be elicited as long as its own neural mone secreted by the testes somehow mod- circuits remain intact. Each of the behav- ifies the functional condition of the central ioral items studied appears to function rela- nervous elements mediating the swimming tively independently of the neural mecha- response. In this respect the hormonal and nism important for the other phases. nervous mechanism is similar to that obtain- Comparing our findings with the extensive ing in mammals where the injection of tes- literature on the neural mechanisms control- tosterone propionate "increases the male's ling sexual behavior in mammals, it appears susceptibility to sexual excitement" (Beach, that some general relationships exist. The 1942b). It has been suggested (Beach, 1942) comparison between the action of the fore- that the gonadal hormones may increase the brain in facilitating the swimming response excitability of a hypothetical "central excit- of the male frog towards the estrous female, atory mechanism" and simultaneously lower and the facilitative activity of the cortex in the thresholds of the integrative circuits controlling the ease of arousal of the copu- wherein the male copulatory patterns are latory pattern in the male rat has already organized. Moreover, there are indications been discussed. that the cerebral cortex contains or is the Beach (1944b) reports that in the rat "the "central excitatory mechanism." Whether, changes produced by forebrain injury in- in Amphibia, the male hormone affects some stead of being specifically sexual, affect re- facilitative mechanism in the forebrain, or sponsiveness to a wide variety of nonsexual acts only on the basic sensori-motor appara- stimuli.... The reduced sexual responsive- tus in the midbrain and lower centers has yet ness of the decorticate male is merely one re- to be determined. flection of a general loss of reactivity to a wide range of environmental situations." A COMPARISON WITH MAMMALS similar situation exists in the male frog. De- In this discussion six discrete phases of cerebration not only decreases the frequency sexual activity of the male have been consid- of the swimming responses of the male frog ered. The clasp response is basically a spinal towards the clasp object but reduces the reflex, but it appears to be regulated and male's responsiveness to other environmental modified by some diffuse generalized activity stimuli, particularly food. of the diencephalon, midbrain, cerebellum, Investigation of the relationship of sub- and medulla oblongata. The warning croak cortical brain centers to mating behavior in is integrated by a midbrain mechanism local- male mammals has not been made, and hence ized in the inferior colliculi, and this response direct comparisons with male Anura are not is relatively independent of the higher possible. Since the sexual patterns of female centers. The sex call is probably mediated by mammals are dependent to a much lesser ex- a midbrain mechanism of a more diffuse na- tent than the males upon an intact cortex ture than that responsible for the warning (Beach, 1944a), numerous investigators have croak. The spawning movements are also studied the effects of subcortical lesions on controlled by midbrain elements localized in female mating behavior. It appears from the tegmentum, and the release of the female these studies that in the female guinea pig, by the male after spawning is dependent upon rat, and cat, the appearance of the female circuits in the pars dorsalis hypothalami, and mating pattern depends upon the integrity of the preoptic area. Although the swimming a relatively small discrete region in the hypo- response towards the clasp object appears to thalamus or anterior edge of the mesencepha- be mediated basically by a neural mechanism lon (reviewed by Bard, 1940; Young, 1941; situated in the midbrain, it is so strongly de- Beach, 1942a). Here we have a rather strik- pendent on the facilitory action of the fore- ing comparison with male frogs where we brain that extirpation of this part of the have described an area of the tegmentum brain eliminates this behavior to a very large which must be intact for the proper perform- degree. ance of the spawning movements. 134 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86

It is conceivable that if one could study major aspects of the male's sexual behavior. certain phases of the sexual behavior of male On the basis of our results, together with the mammals which were not strongly dependent observations of previous investigators and for their elicitation upon cortical facilitation particularly the extensive literature on mam- (or upon previous acts dependent upon corti- malian sexual behavior, we have formulated cal facilitation), discrete subcortical areas some hypotheses on amphibian brain func- might be discovered upon whose integrity the tion. It remains for subsequent investiga- behavior in question would depend. tions to test these formulations in a much In the foregoing experiments we have sur- more rigid and quantitative manner. veyed the effects of brain lesions upon the SUMMARY AND CONCLUSIONS THESE EXPERIMENTS were designed to survey to clasp estrous females was markedly re- the effects of brain injury on certain out- duced, but the swimming reaction was not standing phases of the mating behavior of the completely abolished unless the midbrain was male Rana pipiens. The normal mating pat- also extensively invaded. When forebrain- tern has been described, and the nuclear pat- less males were placed upon ovulated females, tern and other important landmarks of the normal amplexus and oviposition followed. pipiens brain were reviewed briefly. Males with this type of lesion did not release Quantitative records of behavior after var- the female at the end of the oviposition. Le- ious types of brain injury revealed the effects sions to, or ablation of, the preoptic area of various lesions upon: (1) the warning abolished the release behavior but not the croak; (2) the swimming response of the male male's swimming response to the female. towards the estrous female; (3) the spawning Removal of the entire forebrain, dienceph- movements of the male which synchronize alon, optic lobes, cerebellum, and anterior with the oviposition movements of the fe- tegmentum did not interfere with the male's male; and (4) the release of the female by the spawning movements, as evidenced by the male'at the termination of the oviposition. recovery in some instances of fertilized eggs. Qualitative observations were also made on Lesions in the tegmentum at the level of the the effects of brain injuries upon the sex call motor nucleus of the trochlear nerve mark- and clasp reflex. edly disturbed or completely abolished these Ablation of all the forebrain excepting the spawning responses. preoptic area caused no changes in the be- Complete ablation of the forebrain, dien- havior studied. Following the removal of the cephalon, tectum (superior colliculus), cere- entire forebrain (including the preoptic area), bellum, and anterior tegmentum did not in- the tendency of males to pursue and attempt terfere with the mediation of the warning

f11 WARNING CROAK _or R SPAWNING MOVEMENTS J SWIMMINGSWMIGRSORESPONSEE 3 RELEASE FIG. 27. Diagrammatic sagittal section through the brain of Rana pipiens indicating the regions of the brain that were found to be of primary importance for the mediation of each of four phases of sexual behavior. 135 136 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY VOL. 86 croak, but extensive invasion of the inferior nism situated in the diencephalon, midbrain, colliculi abolished this response. cerebellum, and medulla oblongata. The regions of the brain which we have 2. The warning croak is integrated in the found to be important for the mediation of inferior colliculi and is relatively independent each of these four phases of the male's sexual of higher centers. activity are indicated diagrammatically in 3. The nervous mechanism mediating the figure 27. sex call is probably located in the midbrain Qualitative observations indicated that the but is somewhat more diffuse than the warn- sex call sometimes survived ablation of the ing croak. forebrain, diencephalon, optic lobes, cere- 4. The spawning movements are inte- bellum, and anterior tegmentum. The sexual grated in the tegmentum at the level of the clasp reflex was modified by a variety of le- motor nucleus of the trochlear nerve. sions in the diencephalon, midbrain, and an- 5. The neural mechanism controlling the terior edge of the medulla oblongata. It ap- release of the female by the male after the peared that the more extensive invasions and oviposition is situated in the pars dorsalis especially lesions placed farther caudally hypothalami and preoptic area of the fore- modified the clasp reflex to a greater extent brain and is probably related to the auto- than equal amounts of destruction to ante- nomic functions generally attributed to this rior brain areas. region. On the basis of our results, together with 6. The swimming response of the male to- the findings of other investigators, the fol- wards the estrous female is basically a mid- lowing hypotheses have been tentatively for- brain response which is strongly facilitated by mulated: a forebrain mechanism located for the most 1. The clasp response is basically a spinal part in the preoptic area and medial walls of reflex which is modified by a diffuse mecha- the cerebral hemispheres.

LITERATURE CITED ALBERTONI, PETER tional behavior patterns in animals. Res. 1887. Ueber die Hemmungscentren der Krote. Publ. Assoc. Nerv. Ment. Dis., vol. 19, Centralbl. f. Physiol., vol. 1, pp. 733- pp. 190-218. 734. 1940. The hypothalamus and sexual behavior. ARI,NS KAPPERS, C. U. Ibid., vol. 20, pp. 551-579. 1921. Vergleichende Anatomie des Nerven- BEACH, F. A. systems. Haarlem, Erven F. Bohn. 1940. Effects of cortical lesions upon the ARIINS KAPPERS, C. U., AND E. HAMMER copulatory behavior of male rats. Jour. 1918. Das Zentralnervensystem des Ochsen- Comp. Psychol., vol. 29, pp. 193-245. frosches (Rana catesbyana). Psychiat. 1942. Analysis of factors involved in the en Neurol. Bladen, vol. 22, pp. 368-415. arousal, maintenance and manifestation ARIkNS KAPPERS, C. U., G. C. HUBER, AND E. C. of sexual excitement in male animals. CROSBY Psychosomatic Med., vol. 4, pp. 173- 1936. The comparative anatomy of the nerv- 198. ous system of vertebrates, including 1942a. Central nervous mechanisms involved in man. New York, The Macmillan Co. the reproductive behavior of verte- BAGLIONI, S. brates. Psychol. Bull., vol. 39, pp. 200- 1911. Zur Kenntnis der Zentrentatigkeit bei 226. der sexuellen Umklammerung der Am- 1942b. Effects of testosterone propionate upon phibien. Zentralbl. f. Physiol., vol. 25, the copulatory behavior of sexually in- pp. 233-238. experienced male rats. Jour. Comp. 1913. Physiologie des Nervensystems. Pt. II. Psychol., vol. 33, pp. 227-247. Amphibien. Winterstein's Handb. Vergl. 1944. Experimental studies of sexual behavior Physiol., vol. 4, pp. 353-413. in male mammals. Jour. Clin. Endo- BARD, PHILIP crinol., vol. 4, pp. 126-134. 1939. Central nervous mechanisms for emo- 1944a. Effects of injury to the cerebral cortex 1945 ARONSON AND NOBLE: BRAIN MECHANISMS AND MATING IN RANA 137 upon sexually-receptive behavior in the sicht auf die Lebensweise des Tieres. female rat. Psychosomatic Med., vol. 6, Zeitschr. allg. Physiol., vol. 15, pp. pp. 40-55. 15-64. 1944b. Relative effects of androgen upon the EINARSON, LARUS mating behavior of male rats subjected 1932. A method for progressive selective stain- to forebrain injury or castration. Jour. ing of nissl and nuclear substance in Exp. Zool., vol. 97, pp. 249-285. nerve cells. Amer. Jour. Pathol., vol. 8, BECHTEREW, W. pp. 295-308. 1884. Ueber die Function der Vierhtigel. Arch. FLOURENS, J. P. M. f. d. ges. Physiol. des Menschen u. d. 1824. R6cherches exp6rimentales sur les pro- Thiere (Pfltiger), vol. 33, pp. 413-439. pri6ti6s et les function du systame ner- BLANKENAGEL, FRITZ veux dans les animaux vert6br6s. Paris. 1931. Untersuchungen ilber die Grosshirn- GAUPP, ERNST funktionen von Rana temporaria. Zool. 1899. Anatomie des Frosches. Abt. 2. Braun- Jahrb. Abt. f. Allg. Zool. u. Physiol. d. schweig, Friedrich Vieweg und Sohn. Tiere, vol. 49, pp. 271-322. GLASS, F. M., AND R. RUGH BOYLE, ROBERT 1944. Seasonal study of the normal and pitui- 1663. Of the usefulness of natural philosophy. tary-stimulated frog (Rana pipiens). The works of the Honourable Robert I. Testis and thumb pad. Jour. Morph., Boyle. Vol. I. London, A. Millar, 1744. vol. 74, pp. 409-427. BURNETT, T. C. GOLTZ, FRIEDRICH 1912. Some observations on decerebrate frogs 1869. Beitrage zur Lehre von den Functionen with especial reference to the formation der Nervencentren des Frosches. Berlin, of associations. Amer. Jour. Physiol., August Hirschwald. vol. 30, pp. 80-87. HERRICK, C. J. BUSQUET, H. 1921. The connections of the vomeronasal 1910. Action inhibitrice du cervelet sur le cen- nerve, accessory olfactory bulb and tre de la copulation chez le grenouille. amygdala in Amphibia. Jour. Comp. Ind6pendance fonctionnelle de ce centre Neurol., vol. 33, pp. 213-280. vis-a-vis du testicle. Compt. Rendus 1925. The amphibian forebrain. III. The optic Soc. Biol., Paris, vol. 62, pp. 911-913. tracts and centers of Amblystoma and 1910a. Existence chez la grenouille male d'un the frog. Ibid., vol. 39, pp. 433-489. centre m&dullaire permanent pr6sidant 1933. The amphibian forebrain. VI. Necturus. a la copulation. Ibid., vol. 62, pp. 880- Ibid., vol. 58, pp. 1-288. 881. 1933a. The amphibian forebrain. VII. The CROSBY, E. C., AND R. T. WOODBURNE architectural plan of the brain. Ibid., 1940. The comparative anatomy of the pre- vol. 58, pp. 481-505. optic area and the hypothalamus. Res. 1936. Conduction pathways in the cerebral Publ. Assoc. Nerv. Ment. Dis., vol. 20, peduncle of Amblystoma. Ibid., vol. 63, pp. 52-169. pp. 293-352. DESMOULINS, ANTOINB HUBER, G. C., AND E. C. CROSBY 1825. Anatomie des systames nerveux des ani- 1933. The reptilian optic tectum. Jour. Comp. maux a vertabres applique6 a la physi- Neurol., vol. 57, pp. 57-138. ologie et Ala zoologie. Paris, M6quignon- 1933a. A phylogenetic consideration of the op- Marvis. tic tectum. Proc. Nat. Acad. Sci., vol. DIEBSCHLAG, EMIL 19, pp. 15-22. 1934. 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(Pfltiger), vol. 40, pp. 330-351. RUGH, ROBERTS VULPIAN, ALFRED 1935. Pituitary-induced sexual reactions in 1866.' Lefons sur la physiologie g6n6rale et the Anura. Biol. Bull., vol. 68, pp. 74- compare6 du systeme nerveux faites au -81. Museum d'Histoire Naturelle. Paris, 1935a. Ovulation in the frog. I. Pituitary rela- Ernest Bremond. tions in induced ovulation. Jour. Exp. YOUNG, W. C. Zool., vol. 71, pp. 149-162. 1941. Observations and experiments on mat- SCHRADER, M. E. G. ing behavior in female mammals. Quart. 1887. Zur Physiologie des Froschgehirns. (Vor- Rev. Biol., vol. 16, pp. 135-156. ABBREVIATIONS FOR ALL FIGURES III, third ventricle n. op. teg., nucleus opticus tegmenti a. preop. 1. (or lat.), lateral preoptic area n. post. com., nucleus of the posterior commissure a. pret., area pretectalis n. preop. m., nucleus preopticus pars medialis amyg., amygdala n. preop. mag., nucleus preopticus pars magno- aq., aqueduct cellularis cent. gr., central gray n. preop. peri., nucleus preopticus pars periven- ch., chiasma opticus tricularis com. tect., tectal commissure n. sep. 1., nucleus septi lateralis corp. str., corpus striatum n. sep. m., nucleus septi medialis dec. 1. f. b., decussation of lateral forebrain bundle n. subhab., nucleus subhabenularis dec. m. f. b., decussation of medial forebrain bun- n. suprach., nucleus suprachiasmaticus dle n. vent. thal., nucleus ventralis thalami dor. hyp., pars dorsalis hypothalami n. vent. thal. ext., nucleus ventralis thalami pars em. thal., emenentia thalami externa epistr., epistriatum n. vent. thal. int., nucleus ventralis thalami pars f. int., foramen interventriculare interra fim. sep., pars fimbrialis septi post. com., posterior commissure gang. isth., ganglion isthmi post. pole, posterior pole of cerebral hemisphere hab. com., habenular commissure prim. hip., primordium hippocampi hip. com., hippocampal commissure prim. pall. d., primordium pallii dorsalis hyp., hypophysis prim. pir., primordium piriforme inf. col., inferior colliculus rec. preop., preoptic recess 1. f. b., lateral forebrain bundle s. endorh., sulcus endorhinalis lat., lateral ventricle s. intrahyp., sulcus intrahypothalamicus m. f. b., medial forebrain bundle s. lim. hip., sulcus limitans hippocampi N. II, optic nerve s. lim. lat., sulcus limitans lateralis N. III, oculomotor nerve s. med., sulcus medius n. N. III, nucleus of oculomotor nerve s. sep. pall., sulcus septopallialis n. N. IV, nucleus of trochlear nerve s. subhab., sulcus subhabenularis n. Bell., nucleus of Bellonci s. vent., sulcus ventralis n. Bell. neur., nucleus of Bellonci neuropil str. alb. cent., stratum album centrale n. dec. 1. f. b., bed nucleus of the decussation of the str. gr. cent., stratum griseum centrale lateral forebrain bundle str. med., stria medullaris n. dec. m. f. b., bed nucleus of the decussation of str. op., stratum opticum the medial forebrain bundle str. peri., stratum griseum et fibrosum periven- n. dor. thal., nucleus dorsalis thalami triculare n. dor. thal. ext., nucleus dorsalis thalami pars ex- str. sup., stratum fibrosum et griseum superficiale terna tect., tectum opticum n. dor. thal. int., nu,cleus dorsalis thalami pars in- teg., tegmentum terna tr. c. hab., tractus cortico-habenularis n. gen. 1. (or lat.), nucleus geniculatus lateralis tr. olf. hab. 1., tractus olfacto-habenularis lateralis n. gen. 1. (or lat.) neur., nucleus geniculatus later- tr. opt., tractus opticus alis neuropil tr. opt. lat., tractus opticus lateralis n. hab., nucleus habenularis tr. opt. med., tractus opticus medialis n. hip. com., bed nucleus of hippocampal commis- vent. hyp., pars ventralis hypothalami sure vent. opt., optic ventricle n. int., nucleus interpeduncularis z. lim. 1., zona limitans lateralis n. lat. pro., nucleus lateralis profundus z. lim. m., zona limitans medialis n. mes. V, nucleus mesencephalicus trigeminus

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