THAT BREED Occasional Cases Reported, Some of Them with Good Evidence—Two Recent Cases in America—Studies of Germ-Cells Indicate that Chance of Breeding is Very Slight ORREN LLOYD-JONES Associate Professor of Husbandry, Iowa State College, Ames, Iowa

URING the three or four thous- Breeding in 1895, Tegetmier was a and years in which mules have thorough disbeliever in all such cases, D been habitually produced, there but in 1897, speaking of fertile mules, have been many conflicting he mentions a case reported from Mexico statements of fact and theory in regard and says that "this is one of the most to the question of possible fertility detailed accounts of fertility in mules among these . Numerous inci- that has come under my notice," and dents and cases are on record calcu- urges caution in opinionating. lated to prove that mules occasionally exhibit generative powers. The affirm- PREJUDICE IS STRONG ative side of the case may be opened by Skinner (Youatt, 1854) examined the French zoologist Andr6 Sanson very carefully the first-hand evidence in ('88), who uncompromisingly maintains regard to the celebrated Norfolk case of (Vol. Ill, p. 145) the occasional fer- a breeding female mule and proved to tility of female mules. He says "it his own satisfaction its authenticity. does not seem inadmissible that the He also recognized the deep-seated males of the same origin as the females prejudice which people have against which show themselves so easily fertile, giving credence to fertility among mules would not themselves behave simi- for he naively remarks that "Whatever larly," and again "if there are fertile doubt may arise hereafter, there is none males, as we arc sure at present that now, of the truth of this case" (p. 432.) there are fertile females . . ." Sanson's In this case the owner had noticed an claims are unusually broad—most abdominal enlargement in his female writers are more conservative. mule and had adjusted the shafts and N. S. Shailer ('95) comments on the harness to accommodate it, "but never '' singular fact that in only two or three suspected the mother's being in foal cases have mules become fecund." because it was contrary to nature." Cossar Ewart ('93) states that mules On April 23, 1834, she unexpectedly arc generally incapable of procreation, produced a colt. The mule had pre- "though some exceptions to this rule viously pastured with a 2-year-old have occurred." Whitehead ('08) in . Subsequently on August 13, discussing the mule makes the paren- 1835, the same mule produced another thetical remark that '' the cross between colt, a female. Both colts seemed nor- a female mule and a stallion is known to mal, but died when a few months old. have resulted in offspring." Mr. Gun, an English military veter- Stories accompanied by statements of inarian in India, and apparently a eye-witnesses, of the birth of a foal faithful and efficient exponent of his by a mule, and affidavits as to the true profession presents (Field, September nature of the mother, present 17, 1898) in elaborate detail the events obvious difficulties to those who would accompanying parturition in an Indian summarily set aside the whole matter of transport mule. This is indeed a case fecund mules as a thing of myth and hard to refute. anecdote. At the time of publishing Two cases recently reported have the book on , Asses and Mule come before me and I have been able to 494 A WITH TWIN COLTS The large animal here shown is said to be the offspring of a half-blood stallion and a black Spanish jennet, and her twin foals (one of which lived only a few days) are supposed to have been sired by a gray mammoth jack. The colts would therefore be three-fourths ass and one-fourth . (Fig. 5.) collect some evidence on the matter, in the ass has a "rat tail." She has never the shape of statements and photo- brayed like a jennet. Some have graphs. doubted her breeding until they heard One case first appeared in the No- her voice, which resembles more the vember issue of the American Journal neigh of a horse. Twice before the of Veterinary Medicine, Chicago, and present case this female produced foals, again in American Farming for Feb- but in both cases the birth was abnormal ruary, 1916. The facts presented below and the colts died. Dr. L. A. Ray, the were furnished me by the owner and the veterinarian who attended the birth in veterinarian who attended the case. question, says of these earlier foals, J. M. Bryant, of Quincy, Ind., about "They were much deformed and were nine years ago bred a dark chestnut unable to swallow, and one had a double "half blood" Percheron stallion to a head from the eyes down." black Spanish jennet. The hinny thus This "hinny" was bred to a gray produced is now 8 years old, 14)4 hands mammoth jack on July 7, 1914, and on high and weighs 900 pounds. Her July 11, 1915, produced the pair of whole aspect is very ass-like, especially twins shown in the cut (Fig. 5). her hind parts, but Mr. Bryant says The twins were both females. One her head has more the appearance of was 25 inches high, black with white her sire—her ears being dark chestnut points, and lived only 7 days. The color, the same as the stallion. The other was 30 inches high and gray in tail shows a good brush or switch while color. Dr. Ray on February 17, 1916, SUPPOSED CASE OF A FERTILE MULE The female is said to be out of a standard bred by a mammoth jack, which would make her a true mule. Bred to a black Percheron stallion, she is reported to have given birth to the colt shown, which would therefore be three-fourths horse and one-fourth ass. A better photograph of the colt is reproduced in the succeeding illustration. (Fig. 6.) reports this colt as "very peculiar in • Through the courtesy of Glen Hayes, make-up and very unthrifty." A letter editor of American Farming, the follow- from the owner, April 26, reports this ing case was called to my attention; the gray colt (three-fourths ass and one- statements are quoted from corre- fourth horse) as doing well: ' 'she seems spondence with the owner, D. W. to have the large bone of the horse Sullivan, of Weed, Cal. Mr. Sullivan above the knees, and below the knee states that the female in Fig. 6 is out the foot is small like a jack; it shows the of a standard bred mare by a Mammoth Percheron one-eighth in the square hip. Jack. This "mule" was put to a black The colt makes a very peculiar noise, Percheron stallion and on May 31, unlike any animal I ever heard." 1915, produced the male foal shown in Mr. Bryant has bred the "hinny" the picture. The picture was taken this year to a spotted Welsh pony and when the colt was 3 days old. He is hopes to get a foal three-fourths horse doing well at the present writing, and and one-fourth ass. He says he has gives promise of developing into a been about 10 years breeding for a valuable animal. He has a tail like a "grade mule"—and if the present colt mule, and his feet are very small, long lives he believes he will "have the breed and narrow, again a mule-like trait. started." The owner states that "his actions arc 496 A REPUTED "GRADE MULE" The colt pictured in Fig. 6 is here shown at the age of one and one-half years. There is little visible evidence of the one-fourth ass blood which he is supposed to possess; but his owner says that his feet are mule-like, as are his actions. There are physiological reasons for doubting the accuracy of all stories of mules that breed, but many students have been willing to admit the fertile mule as a possibility. (Fig. 7.) more like a mule than a horse. I have trum, but the exact seat of the cause bred this mule again this spring and of this cycle of changes is not clear. she only took the horse once. I think But despite this chain of direct and she will have another colt; if so I intend circumstantial evidence the body of to start a breed of that kind." scientists has always been sceptical, and even mule breeders themselves as a PHYSIOLOGICAL STUDIES class are inclined to discredit reports of The ovaries of equine hybrids have fertility among mules. not been frequently examined as have The negative side of the question is the testes. Ewart examined the ovaries stated boldly by Ayerault ('91), who •of a -horse hybrid of 10 years of unhesitatingly asserts that all cases of age which had died. He found Graffian supposed fertility are errors in observa- follicles present, one of them being V/± tion or recording. He says (p. 152) inches in diameter. A ripe follicle in a that "In Poitou, where 50,000 are 16-hand mare is about 1% inches in annually used for mule production, diameter. "From the appearance of fertile mules are unknown, although this follicle it might well have contained . . . they are in the best possible an almost ripe ovum." This case has condition to be fecundated," since they encouraged Prof. Ewart to say that are constantly pastured with . "occasional fertility among female mules In support of the negative side there is not inconceivable." Habenstreitt are in general two lines of argument worked on the ovaries of a female mule which are followed. and found follicles but no ova. Female 1. All reported cases are cast aside mules exhibit regular periods of oes- as mere myth and anecdote, or as due to 497 WHY THE MULE IS INFERTILE When body cells divide there is no preliminary pairing of . But when germ cells are formed each pairs with its mate as a necessary preliminary to division. In the case of the pure species this is a regular and orderly process as shown in the figure to the left. But in the germ cell divisions of the mule this is impossible as shown in the figure to the right. One trouble is that the hybrid has received nineteen chromosomes from his dam, a mare, and thirty-two from his sire, a jack; and when the chromosomes come to pair off there are not enough of the right kinds to pair. In addition there is an incompatibility between those "pairs" that are present and pairing is difficult or incom- plete. The whole machinery of the cell is, therefore, upset and the cell itself destroyed. Camera lucida drawing, enlarged 3,000 times, from J. E. Wodsedalek (Biol. Bull., XXX, pi. I). (Fig. 8.)

faulty observation, or as due to wrong Frequently horses of mixed breeding interpretation of facts. The cases re- are seen which exhibit asinine traits of ported are so rare that this is not a character, both externally and in dis- difficult undertaking. position. If a female of this nature 2. The germ glands, as well as the became pregnant, she might well be secretions discharged therefrom, of the mistaken for a fertile mule. Such a hybrids are studied histologically and case is doubtless the well-known instance cytologically. These studies indicate a in the Acclimatization Gardens in deep-seated derangement of the cell Paris. A female—supposedly a mule— divisions which would, in normal, fertile produced foals when mated with both animals, give rise to the fully developed the horse and the ass. She was sold germ cells. to the Gardens by some Algerian natives SOME STRONG EVIDENCE who alleged her to be a mule. It developed later that it was extremely 1. As to the first mentioned line of attack calculated entirely to disprove doubtful whether the animal was a mule. fertility among mules, i. e., throwing all The particulars of her parentage, etc., reported cases out of court as errors, are utterly unknown, except as narrated it must be said that the facts as shown by the Algerian horse traders and there above in some cases arc too strongly were, as shown in a photograph repro- supported to be regarded as only duced by Tegctmeier and Sutherland, fiction, and to be cast lightly aside; some but vague suggestions of mule-like way of "explaining" such cases is neces- character about her. Her foals by an sary. Those unwilling to give credence ass appeared to be ordinary mules and to the stories of fertile female mules, were sterile; her progeny by the stallion explain the "supposed cases" in one of were horses which proved fertile. two ways. In fact it is quite possible that the (a) The female may have produced a Sullivan case from Weed, Cal. (Fig. 6). hybrid colt, but the real nature of this belongs in this category. On examining fertile female may not be known. Fig. 6 many readers will doubtless at 498 ORDER GIVES PLACE TO CHAOS At the left is a perfect cell, showing the normal anaphase, half of the chromosomes going to each end. At the right is an abnormal division, due to the fact that the mule (a male, in this case) has not received the same number of chromosomes from each parent. Chaotic cell-division seems regularly to occur in adult male mules, so that all the germ-cells they produce are destroyed by internal causes. It is, therefore, doubtful whether a male mule can ever produce offspring. Camera lucida drawing, 3,000 times natural size, by J. F. Wodsedalek (Biol. Bull. XXX. pi. iv). (Fig. 9.)

once challenge the real hybrid nature of that this case hangs on the other horn the dam. The "rat tail," the sparsely of the dilemma. It is only with con- developed mane, the slightly excessive siderable circumspection that we can length of ear, as well as some lineaments discover evidence in the appearance of of face and body difficult to describe, this female which would enable her to all suggest "mulishness" to be sure, but establish a biological kinship with the unprejudiced observers will pronounce nobler race. her a very horse-like mule. To believers in these cases offer little ADOPTED OFFSPRING difficulty. Tegetmeier quotes Capt. (b) A second way in which supposed Hayes, "a practical authority," as cases of fertile female mules may be saying that "those animals which have accounted for is as follows: been mistaken by superficial observers The female in question may be a true as fertile mules are really in most mule, but the foal which she suckles was cases offspring of mares that have not borne by her. This brings up for previously been bred to donkeys, and consideration the phenomenon of lacta- have given to their foals characteristics tion among female mules. Concerning of their former lovers." Tegetmeier this phase of the question there is little then proceeds to say in regard to the or no debate. Anyone long in a mule above female at the Acclimatization country will have seen cases of true Gardens that "it is not a case of a fertile lactation in mules. To be sure the mule breeding, but that the animal is mammary tissue is normally activated really an ordinary mare whose female by conception, but on the other hand parent was influenced by a first alliance every dairy cattle breeder has seen with an ass." lactation induced in young virgin heifers Even though we do not now accept by constant suckling of a "poorly telegony as a fact, it is clear that here weaned" calf, and even males have is a possible source of confusion in this been known to be stimulated to secrete debated field of fertility among mules, milk. It is not difficult to suppose, for since belief in it by breeders of the past the few cases demanding it, a set of would tend to influence their accounts. circumstances which would enable a Disbelievers may also call Mr. female mule with maternal character- Bryant's fertile "hinny" into question istics to develop active milk secretion on a similar count, but it is interesting at a time opportune for stealing and 499 500 The Journal of Heredity fostering a foal born of a mare—perhaps In point of material his work is com- one lacking maternal instincts. In parable with Ewart's, but in results it is herds of horses and mules it might easily different. happen that a milking mule should Iwanoff worked with two male ze- adopt an orphan colt and give every broids, one 4 and one 5 years old. appearance of being the colt's true Microscopic examination of the seminal mother. discharge showed complete lack of 2. Facts from the second line of spermatozoa, but many round, hard, study, i. e., examination of the cell glancing, refractory, glass-like bodies processes going on within the testis, were present. "In these cases one can- and of the nature of the seminal dis- not speak of degenerate or undeveloped charge, will now be considered. Cossar sperm cells. Ewart probably mistook Ewart was among the first to subject the round glass-like bodies with Brow- the seminal fluid of equine hybrids to nian movement for sperm cells. How microscopic inspection. His hybrids Ewart's observation of a tail twice as were produced by use of a Burchell long as the head, in the semen of his zebra male on pony mares.1 The male hybrid, is to be explained, I cannot say." "Zebroids" thus formed were unable to Suchtet ('96), as the result of his work beget offspring in the many mares to on mule testes, also concludes that the which they were put, though, as is true spermatozoids were replaced by "little of male mules produced in the ordinary round, brilliant, glassy bodies." way, their behavior gave every reason The presence of these round refractory to suppose that they were breeders. In bodies in the semen cannot be gainsaid, the discussion of his work, Ewart but it is questionable if they should be repeatedly mentions seeing incompletely interpreted as "replacing" the sper- formed spermatozoa which were "hardly matozoa. These bodies are probably at all motile due to the tail being only merely masses of hard albumen, and about twice as long as the head, while not cellular bodies at all. Similar in the normal horse and zebra it is fully bodies may be seen in the semen of eight to ten times the length of the normal sheep, swine and rabbits, in head." This seems Eke a case of which there is an abundance of live and arrested development. Ewart inter- perfect spermatozoa. After long stand- preted this lack of motility as evidence ing these bodies seem to absorb moist- that these imperfect sperm cells were ure, increase in size, lose their refractory unable to make any headway against properties and disappear. It is possible the outward currents which exist in the that the testes of the mule play little or generative tract of the female. As a no part in furnishing the seminal dis- result they never reached the ovum, charge, but that it is secreted by the were of no use, and the zebroid was accessory glands of the generative tract. sterile. Stephan in 1902 reported some studies DEGENERATIVE CHANGES on the structure of mule testes. Some of Iwanoff also made some observations his material was taken from castration on the histological structure of the testis operations and some from animals of the mule. He found tubules of which had died. His studies were greatly reduced diameter, comparable histological rather than cytological. to those seen in sexually immature He reports an almost complete absence stallions. He reports excessive numbers of seminiferous tubules, a great exag- of Sertoli cells, many degenerative, as geration of "parenchyma" tissue,and well as degenerative spermatogonia. many other unusual features. He also notes the presence of white In 1905 appeared Iwanoff's "Unter- leucocytes within the tubules, which, to suchungen uber die Ursachen der Un- his mind, play a part in the degenerative fruchtbarkeit von Zebroiden." processes going on there. These obser- 1 For an account of the production of zebra hybrids see "The Grevy Zebra as a Domestic Animal," by George M. Rommell. American Breeders' Magazine, Vol. IV, Xo. 3, pp. 129-139, November, 1913. Lloyd-Jones: Mules That Breed 501 vations are in line with those of Guyer mare on the one hand, and sperm of ('00) on sterile hybrid pigeons. Iwanoff the jack on the other, mitosis and further reports abundant parenchyma cleavage processes are apparently undis- and interstitial cells, and emphasizes turbed, for growth and development of the secretory nature of these tissues, the fetus and of the foal proceed nor- holding them accountable for the second- mally. ary sex characters of the mules. Whitehead ('08) also reports work on CAUSE OF STERILITY testis structure in mules. He found no As far as can be seen there is nothing secondary spermatocytes and no sperma- irregular in the growth or cell divisions tozoa of any kind; interstitial cells were of the mule till he reaches sexual ma- abundant and granular. Whitehead turity. Up to this time maternal and had examined the testes of cryptorchid paternal chromosomes have lain side by horses and found them to be similar in side and carried on their customary structure to those of the mule. He functions. There has been no necessity puts the scrotal testis of the mule in for them to cooperate to any noticeable the same category with the abdominal extent, each chromosome has divided testis in cryptorchids of pure species. at mitosis independent of the others, Sexual passion is quite apart from sexual one-half going to each daughter cell. fruitfulness, mules and cryptorchids The real conflict ensues during the exhibiting the former in marked degree. various stages of the primary sperma- Like Iwanoff, Whitehead says that tocyte. Normally at this stage there sexual passion is due to specific internal is a pairing and subsequent separation secretions of the interstitial cells. '' They of homologous chromosomes from father are the only cells which can elaborate it and mother. In case of the mule, how- for the only other secretory cells are ever, because the ovum and sperm con- degenerate, while the interstitial cells tributed such unequal numbers of are hypertrophied."2 chromosomes, there are many chromo- The most recent, and detailed work somes without a homologue with which on the structure of the mule testis is by to mate, and even in case of homologues Wodsedalek ('16). He has carefully the physiological ^compatibility of the followed the cell cycle in the mule testis, two plasms render the pairing difficult and, carrying out the suggestions of and incomplete, or prevents it entirely. Guyer made for pigeons in 1900, has "So great is this disturbance that the offered a specific explanation for the destruction of each cell is inevitable abnormalities seen in the testis, which and no spermatozoa are produced, result in sterility. Wodsedalek had causing the hybrid to be sterile." It is previously reported ('14) thirty-eight as plain that the evidence drawn from such the chromosome number in the mare— studies makes the likelihood of these each ovum carrying the haploid number animals begetting offspring extremely nineteen. From his study the above small if not altogether negligible. author concludes that a plausible However, it would seem wise to be chromosome number for the jack (male conservative and tolerant. Several cases ass) is much greater than the horse, have been reported where there is a namely sixty-five, each sperm carrying regular and orderly disappearance of thirty-two or thirty-three. As a con- sperm-forming cells. For instance, sequence the fertilized egg destined to Morgan has shown that in certain gen- produce a male mule shows fifty-one erations of Phylloxerans, in spermato- chromosomes, nineteen from the mare genesis, half the spermatids (those lack- and thirty-two from the jack. (It is as- ing the accessory chromosome) regularly sumed that the female mule would show degenerate. The disappearance of these fifty-two.) Despite the great diversity cells is precise in nature, and occurs in an in the nature and number of the chromo- orderly fashion at a fixed stage in the somes contributed by the ovum of the cycle of divisions. Apparently, how- 1 Miss Boring {Biol. Bull., XXIII, pp. 141-153), working on the testis of the fowl, failed to find evidence in support of the view that interstitial tissue is responsible for secondary sex characters. 502 The Journal of Heredity

ever, the abnormalities seen in the cell relief and joy. But such animals are divisions in the mule testis are not pre- not as yet staple market commodities, cise in nature, but occur in a haphazard for whatever the true situation in regard fashion, as a result of a tangled con- to mules occasional!)' producing off- fusion of cell elements—it is not incon- spring may be, one thing remains cer- ceivable that a chance series of divisions tain, namely, that as far as the breeding might give rise to a germ cell able to industry is concerned, we must as yet cause conception in a fertile female. take our mules half-and-half in the way Moreover, it must be noted that it is that Homer and Varro described several extremely seldom indeed that male thousand years ago. mules are allowed to come to the age of maturity without castration, and it is LIST OF REFERENCES even more seldom that they are allowed AYRAULT, EUGENE.—De l'lndustrie Mulas- to breed mares. Therefore there is very siere. EWART, COSSAR.—1899. Penycuick Experi- slight opportunity to put their breeding ments. powers to a test. GUYER, M. F.—1900. Spermatogenesis of It should be further remembered that Normal and Hybrid Pigeons. Univ. Cin- cinnati, Bulletin 22. in practically every case these micro- IWANOFF, E.—1915. Untersuchungen uber scopic studies have been made on the die Ursachen der Unfruchtbarkeit von germ gland of the male. It is conceiv- Zebroiden. Biol. Cent. 25: 789-804. able that matters might occasionally SANSON, ANDRE.—1888. Traite de Zootechnie, proceed differently in the ovary, where Tomes 3-5. SHAILER, N. S.—1895. Domesticated Ani- a different chromosome constellation mals. exists. This would result in a condition STEPHAN.—1902. Sur la structure histologique where female mules might at rare inter- du testicule des Mulets. C. R. d l'Assoc. vals possess generative powers but d'Anat. IV, Montpellier (quoted by Iwanoff). TEGETMEIER, W. B. and SUTHERLAND, C. L.— males never. 1895. Horses, Asses, , Mules and There may be some uses for which a Mule Breeding. London. mule that is only y± horse might prove WHITEHEAD, R. H.—1908. Function of Inter- valuable, and certain it is that there are stitial Cells of Testes. Anat. Rec. 2:177. many occasions where a mule that is WODSEDALEK, J. E.—1916. Causes of Sterility ass in the Mule. Biol. Bulletin XXX: 40\ only )4 would be welcomed with pis. i-ix.

IRIS BREEDING RISES have been little used by have yet to obtain a seed from a real students of genetics, probably be- German iris. I cause other plants can be grown in "The method of procedure is simple. less space and time. Pollinations I remove the stamens from the bloom are easily made, however, and any to be cross-fertilized, before the pollen amateur of this genus might well try sacs open, and apply pollen to the lip his hand at crossing some of his favorite of the stigma by rubbing it with a forms. Miss Grace Sturtevant of Wel- pollen-laden anther from the bloom lesley Farms, Mass., contributes the used in making the cross. This covers following suggestions of technique: the surface with pollen so well that there "The irises with which I have worked is little danger from other pollen, but have been the hardy varieties which to make matters sure the bloom can be could be grown without protection or protected for a short time, or the falls especial treatment in my garden; thus removed so that no wandering bee can limiting the scope of the crossing in a crawl in beneath the arching style-arm. large degree to what are known as I usually remove the rest of the buds German irises, though truth to tell I on that branch and label it.