Deep Scattering Layer Migration and Composition: Observations from a Diving Saucer
Eric G. Barham
Science, New Series, Vol. 151, No. 3716 (Mar. 18, 1966), 1399-1403.
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http://www.jstor.org/ Tue Nov 23 04:04:412004 References and ~otes frequency bands. This strongly implies their daytime depths, and apparently
1. W. J. H. Nauta and P. A. Gygax, Stain resonant scattering from bubble-con- the French bathyscaphe dives have also Techuol. 29, 91 (1954). taining organisms (8). Recently, direct been confined to daylight hours (13). 2. P. Glees, J. Neuropath. Exp. Neural. 5, 54 (1946). observations from the bathyscaphe With the Cousteau Soucoupe Sous Ma- 3. - and W. J. H. Nauta, Monatsschr. Trieste showed that another type of rine "diving saucer" (14), four dives Psychiat. Neurol. 129, 74 (1955); D. H. L. Evans and L. 14. Hamlyn, J. Anat. London organism at the opposite end of the were made on 3 and 4 February 1965, 90, 193 (3956); D. Bowsher, A. Brodal, F. Walberg, Brain 83, 150 (1960). phylogenetic scale, siphonophores of in about 1300 m of water, approxi- 4. R. P. Eager and R. J. Barrnett, Anat. I
IS MARCH 1966 mounted, UQN 12-kcy/sec transducer, rate of rise just at sunset. From this the skiff, and adjustments in saucer a Gifft Precision Sonar Transceiver run point, upward migration was com- depth were made accordingly. During it high gain with a 0.017-sec signal pleted in about 2 hours. On two of ascent and descent of the saucer, al- length, and recorded on a Precision the observation days, weak, discrete most continuous observations were Depth Recorder model V. Heavy sur- sound reflectors (15) were present made with the use of two 1000-watt face scattering was present at night. above the main layer and rose ini- flood lamps and a 150-watt spotlight. At dawn a layer separated from the mediately above it, masking any pos- TO avoid attracting or repelling ani- surface zone and performed a dra- sible evidence of re-formation of an mals while the saucer was hovering be- matic downward migration of ap- upper layer. Diffuse scattering record- lore, during, and after passage of the proximately 300 m in 90 minutes. ed at high gain also contributcd to layers, series of 2-minute observations (Figine 1 presents the echogram oh- this masking. At dusk the lower layer were made with the lights on, alternat- tained on 4 February during the time rose rapidly, at a maximum rate of ing with 3-minute waits in darkness. of saucer dive 3, and is typical of the 12 m/min, eventually fusing with the For the first 1% minutes of the ob- morning migrations.) When the mi- main layer. The nature and behavior servational periods, the regular flooil giation was about two-thirds complet- of the layers during the 3 days of 017- lamps were used. An additional 2.5-kw ed, a diffuse upper layer split from servation were essentially the same. "movie light" mounted at the end of the main layer at the 220-m level Slight variations could be attributed an extendable arm was turned on for and disappeared from the record. Si- to changes in the gain settings of the the last 30 seconds of the observa- multanco~~sly,a lower layer separated, transceiver and recorder, and extrane- tion periods. In Figs. 2 and 3. respcc- dropped down to a depth of 420 ni, ous noise. tively, numbers of myctophids and ind faded out. Indications of two com- During the dives, personnel in a physonectid siphonophores Lire shown ponents were evident in the main skiff, using a directional listening de- at the time and depth they were sighted layer during its downward migration. vice, tracked the position of the saucer ~li~ringciives3 and 4. I hese components then merged as the by its 37-kcy/sec pinger. Cotiimunica- Dive 3 started before dawn, while layer leveled off at about 300 ni. Dur- tions between the skiff and saucer were the deep scattering layer was still at ing late morning the main layer made at 20-minute intervals by tinder- the surface (Fig. 2). A concentration thinned, again showed a suggestion of water telephone. Movements and of myctophids, one of three possible two components, and became unre- depths of the layers were recorded by species, referred to here as the "silver cordable during midday. Evening as- the RV T-441 within a mile (1.6 km) n~yctophid" (16), was observed from cent of the main layer began gradually radius of the dive site. This informa- 30 to 110 ni. These were aduli fish ill mi~laftcrnoon with 'In increase in tion was transmitted to the saucer via ranging from about 8 to 10 cm in length. Between 50 and 60 m, they swarmed in the saucer lights, swim- ming in ;i series of quick, random movements of about I 111, alternating with motionless, short pauses. They avoided the brightest region of the light field and were repelled by the MYCTOPHIDS V movie light. A few lantern fish fol- lowed the saucer downward, and the lights were briefly turned off to dis- courage their departure from their nat- ural depth. After the saucer leveled off at 190 m to begin the series of 2-minute observations, three mycto-
PHYSONECTS 4 phids were seen before the layers nii- grated past the saucer. These were a different species from the near-surface popukition and were motionless, sus- LIGHTS ON a OFF* penitcd vertically, he:id down (16). Eight silver myctophids were seen during pas- sage of the layer, swimming downward at ;I 45' angle. Ignoring the saucer lights, they made rapid flights of several meters, paused monientarily, changed Pig. 2. Distribution and numbers of myctophids and physonect siphonophores observed direction, and continued downward. The during downward migration of scattering layers during dive 3. The time scale of the top of the main layer had leveled original precision depth recorder echogram represented by Vc 1 has been compressed off ;it 278 m. As the saucer descend- 6 to 1. Depth course of the saucer was established by its upward-direclod Alias echo sounder pinging on the sea-air interface. Its trace has been converted to the same ed to 275 m, five silver myctophids depth and time scales as the diagram. The open bars represent periods when the swam upward into view. At 300 111, liglils were on; the black dots, times when lights were off. Depth checks of the sLiucer large numbers of this species swarmed were made by recording the saucer on the RV T-44 1 echo sounder, and the presented in the saucer fights. Their actions were depth trace is considered accurate within tlie limits of the open bars (about 10 ni). Numbers of myctophids sighted are shown above the depth course; the physonccts, similiir to those observed at ihe snr- below. ftice. As the saucer ascended, several of the fish followed upward, apparent- ly drawn by the lights. The floods were turned off. At 258 m, when lights were turned on momentarily, no myctophids were seen. At 210 m, ambient light was discernible, and the lights were once again switched on. From 100 nl to the surface, increased ambient light reduced the effectiveness of the lamps and limited the field of vision. Three types of physonectid siphono- phores wcre observed: (i) a large spe- cies, about 60 to 70 cm in stem length when fully extended, and similar in "Â¥I, appearance to Nanomiu (= Stepha- LIGHTS: ON D OFF 0 nomia) hiju,ga (16), but with fewer feeding individuals (gastrozooids); (ii) smaller forms (20 to 40 cm in length), 1 I I I 1 I t I 1930 1900 1830 1800 1730 1700 1630 1600 either younger colonies of the same, TIME or a closely related species; and (iii) Fig. 3. Distribution and numbers of myctophids and physonect siphonophores ob- a small (20 to 30 cm) form, lacking served during upward migration of the layers during dive 4. Treatment is the same concentrated pigmentation in its zooids. as in Fig. 2. These will be rclerred to, respectively, as "large Nunoinfa type," "sn~all Nunomiu type," and "small pelucid boas structures, which I took to be tom part of the main layer and the type." their pneumatophores, sccmed to col- lower laycr (Fig. 3). About half of On descent 01 the saucer, a mixed lapse and fall to one side. No other those observed were the large Nunomia population of physonects was centered physonects were seen for the duration type. These were rising rapidly in ap- above the silver myctophids at 35 m of the dive. proximately the reverse posture of (Fig. 2). Some were swimming straight Dive 4 began in late afternoon, when those seen descending. I got the im- down. Those observed at 180 to 200 the main layer had risen about 100 pression they were revolving slowly m, before the layers had migrated m from its midday position (Fig. 3). around their stem axis. Their half-con- downward, were small, inactive Nano- Only one questionable myctophid was traded stems streamed behind like a inia and pelucid types. The three seen at the edge of the light field dur- tail on a kite at a lesser angle than siphonophores seen at the time of pas- ing descent, and only one small phy- their actively pumping, more erect sage of the bottom of the layer were sonect was seen during the second ob- anterior end. They were always ob- the large Nunomla type. When they scrvation period at 105 m. Over the served slanting away from the light were actively swimming down at about next hour, 12 observation periods were field. Some of the smaller Nunomia a 45' angle, with tentacles contracted devoid of either type of organism. types wcre undulating from side to and stems half drawn up, their motion Just as the upper part of the main side, indicating asynchronous contrac- was straight and continuous, typical layer passed the saucer, silver mycto- tions of nectophores (17). They were of synchronous contractions of the phids wcrc sighted. At first only a distracted by the lights, and some, by swimming bells (nectophores) (17). few were seen, but their numbers in- further contractions of their stems, as- Their rate of descent was more rapid creased as the middle of the main layer sumed a horizontal swimhing posture than that of the myctophids. A mixed passed. Their counts then dwindled or turned in large irregular circles. .population of large and small abruptly. The behavior of the lantern As the saucer ascended slowly on Nanoinia types was observed during fish was strikingly different from that its jets, four physonccts were observed passage of the main layer. Their swim- displayed during their downward mi- at 70 to 60 in. Between 30 to 20 m. ming actions were similar, and they gration. They were swimming in slow, the saucer was surrounded by the silver displayed a mild avoidance response zigzag motions, of about 2 m. Some myctophids. They swarmed in our to the lights. The last three siphono- were swimming upward at about a lights and were attacked by squid. phores, observed at the time of pas- 45O angle; others wcre almost hori- The relationship of myctophids and sage of the upper layer, were of the zontal. The fish appeared to be mildly physonects to scattering layers can be small pelucid form. These could be attracted to the lights. None were summed up as follows. During dive 3, seen only when close to the observa- sighted during the passage of the low- made through the layers at the sur- tion port when the movie lights er laycr. The four myctophids seen af- face, while the layers were descend- were on. They swam downward, an- ter passage of the layer were smaller ing, and in the top of the main layer terior end leading, in spirals about and sluggish in action, and their scales at its daytime depth, at least 233 1 in in diameter. As they entered the did not reflect light as strongly as those myctophids were sighted coincidentally brightest region of the light field, they observed in the main layer. They ap- with scattering layers, and six at other reversed their position, twisted into a peared to be a different species (16). depths (three of these were attracted double spiral, spread their tentacles, Physonect sightings were concentrat- upwards from the depth of the layer and hung motionless (18). Apical bul- ed at the times of passage of the bot- by the saucer lights); 49 physonects
18 MARCH 1966 were sighted in relation to the layers, ed to radii of free spheres (1.9 to References and Notes 1. E. M. Kainpa and B. P. Botlen, Nature 174, atid nine elsewhere. Duringdive 4, 3.4 mm). It is of interest to relate 869 (1954); R. H. Backus, Jt. C. dark, Jr., A. niiidc while layers were ascending these dala to the detailed acoustic S. Wing, ihid. 205, 989 (1965). 2. G. L. Clarke and R. 13. Backus, Bull. Znvt. and after they had surfaced, at least analysis of deep scattering layers in Ocetinogr. Monaco 64, No. 1318 (1964). 161 myctophids were observed in the the Atlantic by Hersey, Backus, and 3. C. F. byring, R. J. Christensen, R. W. Raitt. ./. Acuust. Sue. Am. 20, 462 (1948). layers, and live at 100 to 200 in at Heilwig ((5'). Theoretically (22). the 4. M. W. Johnson, J. Marine Res. (Sears Found. other times; 45 physonccts were in swim bladders of the silver myctoph8ids Miirine Kex.) 7, 443 (1948). 5. J. B. IIersey and It. H. Backus, in The Sea, phase with the layers, and five werc would fit these authors' "mid-frc- M. N. Hill, Ed. (Wiley, Ney York, 1962). vol. 1, p. 498. ;it 100 to 200 m at other times. Re- quency" layer whose peak resonance 6. N. B. Marshall, .I.Marine Res. (Sears Fuunil. sults of dives I and 2 made at the varied between 6 and 11 key/sec, and Marine Res.) 10, 1 (1951); G. H. Tucker, ihid. 10, 215 (1951); E. G. Barham, thesis, same times on the previous day werc changed as the 1/2 power of the Stanford University (1956). essentially similar. Other organisms frequency during upward migration 7. N. B. Marshall, 1)iscin ery Rep. 31, 1 ( 1960). 8. .I. B. Hersey, R. H. Backus, .I. Ilellwig, Deep- capiiblc of scattering 12-kcy/sec sound (their equipment was Frequency limited Sea Re:,. 8, 196 (1962). were observed (for example, squid. during downward migration). They 9. I,. H. llym;tn, The Invertebrates (McCiraw- Hill, New York, l941), vol. 1 pp. 467-485. hcteropods, euphausiids, sergestid suggest this would indicate a causative 10. I?. G. Rarliam, Science 140, 826 (1963). 11. G. V. Pickwell, E. G. Barham, J. W. Wilton, shrimps, pelagic crabs, and unidentified organism capable of maintaining a ibid. 144, 860 ( 1964). fishes). None, however, were spatially constant gas volume (23). Extrapolat- 12. [. B. Andrecva and Yu. G. Chindonova, Olu-unolugii-a I, 1 12 (1964). related to the laycrs. ing from previous measuren~ents of 13. "R6sultats ScientiIiqiie& des C'ampagnes du One cannot enter an environment physonects (10, I/), bubbles within Bathyscaphe F.N.1t.S. Il I, 1954-1957," Ann. lust. O(+uno,yr. Paris 35, 235 (195.8). without modifying it. The saucer lights Ncinomia-type siphonophores closely 14. Descriptions and pictures of (he saucer are in appear to have been the main stimulus correspond to their "high-frequency" .I. Y. C'onsleau with J. Dn"an, The l.ivinv Sni (Harper and Row, New York, 1963), p. affecting the behavior of the organisms laycr. In these cases, peak resonance 278, and It. S. Dietz, The Sea, M. N. Hill, P,d. (Wiley, New York, 1963), vol. 2, p. 507. (19). The differences in phototactic varied between 15 and 25 kcy/sec and Use of the saucer in marine geological in- response of the fish and physonects changed as the 5/6th power of the vestigations is reported by F. P. Shepard et a/., Science 145, 1042 (1964). Dives reported obviously influenced their observed hydrostatic pressure; this was inclica- liere were made uncier :I lease agreement with abundance (20). Regardless, edicient tivc of expansion and contraction of Westiii~ioiise-Cousteau. 15. IIigh-resolntion echo sounders frequently re- sound scatterers need not be present gas bubbles, and would be more prob- cord a strong individual target in the form of in large numbers to account for the able in physonects rather than fishes, a hyperbola These are generally located at daytime depths above the deep scattering layers (3, and many of the orga- since pncumatophores arc capable of layer and migrate upward just above tho layers. See R. S. Dietz, Sci. Am. 207, 44 nisms were seen when the lights were stretching, and excess gas can be. (An" l962), and Mersey and Backus (5). first turned on. The striking correla- vented. 16. Since I lacked a method of collectino, mid- water organisms from the saucer, specific tion of their ~1,istributionwith the lay- A significant difference between re- identification of i'anna unfamiliar to me was ers is convincing evidence that we are sults reportcd here and those made impossible. At the time of the dives, RV T- 441 personnel dip-netted under ;i night light dealing with the causative scatterers. from the Trieste in the California Cur- nd made plankton tows with a 0.5-m net. Very probably, the silver myctophids rent (10) is that the spatial rclation- Squid, eupliansiids, and sin-imp werc titken, but no myctophids or pl~ysonects. llcwevcr, werc [he primary cause of the main ship between myctophids and physo- excellent motion picture footage of the latter nects is reversed. In the earlier study, orginisms was obtained from the saucer. Iiiycr. These were concentrated in its These tilnis were viewed by E. 1-1. Ahlstrorn upper component. The lower compo- physonect,~were associated with a main of the Biircii~i of Commercial tishcries. and C. L. I-Inbbs and niyctuphid specialist R. I,. nent of the main layer and the lower layer at a daytime depth of 300 m, and Wisner of the Scripps Institution. In Wisner's layer appear to be associated with the myctophids (Slenohraclii~~,~[-Laitii~itz- opinion, based on size, shape, behavior, and vertical and geographical distribution, the ~Vanotr~ia-typephysonects, the large yctzi,~]leiicopsur~~s and L. iite.victinns) , myclophid in question is one oF three species, ,\(ition& type predominating in the the adults of which lack large, function- f.iinipcinyctns onio,st;ynia, I,. purvicnuda, or most likely Mj~ctoplium uurolnlfr~iutttin. For alter feature. (Because of depth iimita- al swim bladders, were concentrated the purpose of this report, because of its propet ties, I refer to it as 111. light-reflecting tion of the saucer we were not able between 450 and 700 More recent, "silver myctophid." The smaller, bicick, quies- to penetrate these components at their unpublished data show that in the sum- cent species seen in low numbers out of phase with the 1:iycrs resembled 7.. iuexicfinnv. On daytime depths.) The small, pelucid mer months these fishes are frequently the basis of viewed motion picliire tiliiis and physonccts may be the cause of the associated with a deep layer recordable geographic distribution, A. Alvarino of the Scripps Institution si~ggests that the large ill-defined upper layer, but the obscr- only by 12-kcy/sec echo sounders as it Nufioinifi-type physonect is probably Hfilis- valions are far from conclusive on migrates to the surface. These arc prob- tta,iinici (=. Slephanortiiu) rnbr;~. 17. G. 0. M:ickic, Pror. Roy. Soc. l.ofiiltifi Star. this point. While individual mycto- ably the populations sa11iplei.i long ago IS. 159, 366 (1964). Off San l)icgc), 1 have ;ilso observed Nunomia !)ijn&ti from the saucer, 01 by Tucker's (6) net hauls. whereas his -ihids physonects were not followed nii";:itit~g downward in a scattering layer i11 (hi-oiighout the course of vertical mi- shallower layer. attributed to txiphci~i- ;in upright position simihu- to th:it described by Mackie as "reverse swimming." However, gration, again the correlation of popu- siids, was probably caused by physo- the siplicinosome was contracted to one side lalions with movements of the layers nects. in :in "S -3- shape. A series of r:ipicI nectopliore pnls;-ilions ietted the colony downward ab~ut caves little doubt that they do undcr- Investigations by deep submersihlcs :i meter at a time. Brief rests would follow take these journeys. in other water-mass regimes should thebe movements, and the colony would rise slightly, which indicated positive buoyan:y. Dissections of three specin~cns of provide additional information on the These alternating swim and rest actions con- tinned until the colony disappeared from view each of the three possible silver mycto- relative importance of these two types below me. phid species demonstrate that all have of scatterers and identify other cansa- 18. A similur behavior has been observed in captive calycoplioran siphonophores and term- well-developed, prolate-shaped swim tive organisms. ed the "veronica" display hy G. 0. Mackie bladders with large gas glands (21). ERICG. BARHAM ancl D. A. Boag, Puhhl. Stuz. Zool. Napoli 33, 178 (1963). To conveniently evaluate these swim Marine /Â¥;n~)it,otzmenDivision, 19. While adjusting ballast, or maneuvering, the bladder sizes as acoustic resonators, U.S. Navy Electronics Laboratory, saucer creates a loud, low-frequency noise. None of the organisms appeared to be af- their computed volumes were convert- Saw Diego, California 92/52 footed hy the din. SCIENCE, VOL,. 151 Differences in light-reflecting pig~ilentation of the pregnant rat is intensified licking the organisms is also a factor in estimating relative population densities. For example, of her own ventral surface. Recently when Rood lamps were used, I estimate that we reported that licking of the nipple the silver myctophid could be seen ;11 dis- tances up to 7 In; the large Nufiomic/-type lines and of the genital and pelvic pliysonect with orange-pigniented gi~strozooids was recogniztible at up to 5 m; and the small regions increases markedly with the Nfii~miiiu-type could be seen only at disttinces advance of pregnancy, whereas lick- of up to 3 m. The half-angle of the cone of vision from the saucer port is about 45' in ing of the more anterior body parts, water; thus these volumes compute to 359, of the head, forepaws, shoulders, and 13l, and 28 ni:\ respectively. Use of the movie light at least doubles these distances and upper back, tends to decline (3). the volumes increase eight times. I did not Since sensory stimulation is ncccs- keep a separate recon1 of sightings while using the regular floods and (lie movie light. sary for postpartum mammary f~inc- Fig. 1. A pregnant rat weal ing a full collar. Because of these variables, 1 have not at- tempted to reduce numbers of organisms oh- tion, and since self-licking is prominent reto a common volume denominator. in the behavior of the pregnant rat, Examination of specimens provided by R. L.. Wisner was done by I<. C;tpen. Descriptions it seems reasonable to ask whether self- dehydrated and cleared, and embedded and measurements of these and other ha- licking stimulates mammary develop- in paraffin before being serially see- thypelagic fishes are in m:muscripl. U.S. Nail. Defense Res. Committee Lliv. 6. ment during pregnancy. Mammary de- tioncd at 5 ,, and stained with henia- Suminuv Tecli. Kept. (1948). vol. 7. Andreeva velopnient was assessed at the end of toxylin and eosin. One section from and Chindonova (!2) have recently consid- cred the sheer modulus etTect on bubbles, gestation in rats that had been pre- each gland was chosen randomly when- which theoretically enhances resonance at 300- to 400-m depths. vented from licking theniselves through- ever the developmental level was as- J. Kiinwisher and A. El?elin& l)c~,/p-Sea Re',. out pregnancy and in several groups sessed. 4. 211 (1957). have ilnestioned, on a physi- ological basis, whether physoclisto~is, swim- of controls that had been allowed to As a measure of mammary develop- bladdtred fishes can secrete and absorb gas lick. ment, the proportion of secretory tis- rapidly enough to maintain neiitr;il buoyancy tliroi~hout their vertical r;mge. In this re- The main group of n~~lliparo~~spreg- sue to total glandular tissue was ob- spect, note that the silver myctopliids oh- nant rats (4) were prevented from tained by projecting the irnage of a served on their downward migrations were swimming rapidly. In eontr;tst. their upward licking by attachment around the neck section on a paper of uniform weight swimming was more leisurely, and upward of an 8.7-cm-wide full rubber collar and by tracing the image in detail; the migration of the main layer associated with these fish was slow. never exceeding 2 m/min so designed that the female could not area representing the entire gland sec- and taking sever;!I hours to complete. 24. I thank I<. Kientzy for skilled saucer pilot- extend her head beyond the collar's tion was then cut out and weighed, ing, and N. Shenton and the Westingho~~se edge and lick her ventral surface as were the smaller areas representing team for logistic sunport. R. Niihigin, W. Bunton, R. Bradley. and I. Ilavics :~ssisted (Fig, 1, 5). secretory tissue. Secretory tissue was in operations at sea. .1. Flynn aided annlvsis To control for the burden of wcar- thus determined as a weight percent- of data. Ci. Curl, F.. Buflington, W. Batzler, 0. Prible, 1:. Hamilton, and G. Pickwell have ing a full collar, a second group wore age of the total gland section. This given iidvice. Conversations with R. Backus weighing method is comparable to have been helpful. notched collars, equal in weight to the a standard planimeter technique (8) ; it 17 January 1966 full collars but having 5-cn~ notches cut out to allow the females to reach yields results that correlate positively under the collar and lick their bodies. with ratings of the density of alveoli A third group, uncollared throughout within the lobules, as well as with the Mammary Glands of Pregnant Rats: pregnancy, provided normative data amounts of secretion within them. Development Stimulated by Licking on mammary development. Figure 2 shows that the mammary Because the fu!! collar not only pre- glands of full-collared rats contained Abstract. At the end of gestation, vented licking but also interfered with only about half as much secretory tis- the inannnurj~glands of pregnant rats various normal behavior patterns, in- sue as those of each control group. /11ul have been prevented from l/ck//~g terference that could cause stress (6), An analysis of variance for all groups their ventral surfaces by neck collars it was necessary to add another con- was significtint (I7, 36.23; p<.OOJ), are about 50-percent less developed trol group in which licking was allowed as was the difference between the full- than those of control animals. Neither but in which stress was present. This collared group and each control group, the burden nor the stress effect of [lie fourth group therefore wore no col- revealed by Duncan's new multiple- collar is an alternative explanation. A lars hut were injected twice daily with range test at the 1-percent level. considerable proportion of inammarj1 0.25 ml of 2-percent formalin, a pro- Since the notched-collared group did development dz~ring pregnancy is [lm.'i cedure reported to produce a stress re- not ditTer significantly from the uncol- caused hy the female's own licking. action shown by enlargement of the lared group, the burden of the collar is adrenal glands, without interfering with Although suckling and other stini~~l~i-pregnancy (7). A fifth group, injected tion of the ventral surface of the rat with distilled water, served as controls arc known to maintain lactation and on the formalin injection. cause mammary growth after parturi Samples of mammary gland were lion, there is no evidence that sensory obtained after the females had been stimulation contributes to mammary killed on the 22nd day of preg- developnicnt during pregnancy (I). nancy, just prior to parturition. The Yet by the time the female gives bi~th left abdominal mammary gland was her mammary glands have increased removed and fixed in 10-percent for- considerably in size and have begun to maldehyde solution for 24 hours; a produce milk (2). 0.5-n~m piece of tissue close to the A striking behavioral feature of antcriorn~ostnipple was then cut away,
18 MARCH 1966