SPERM FORMATION 



7 



division cells (Figs. 8 and 9) and thus mature 

 sperms (Fig. 11) with 5 (5 double) and 7 (5 

 double plus the two sex-chromosomes) chro- 

 mosomes respectively. Assuming the woman 

 (negro) to have 24 chromosomes — that is 12 

 after they have been reduced ready for fer- 

 tilization — we can readily predict the sex of 

 the offspring of each cell. If the sperm 

 carrying the twelve chromosomes (Fig. 11 — 

 first two sperms) should come in contact 

 with a human egg (Fig. 16), a new cell (Figs. 

 12 and 13) and later an embryo having 24 

 chromosomes would be formed. This would 

 of course be a female, since the male has only 

 twenty-two chromosomes, while the union of 

 a sperm having only 10 chromosomes (Fig. 11 

 — last two sperms) and an egg would result 

 in an embryo of 22 chromosomes — a male. 



Wodsedalek (1913) has clearly demonstrated 

 the presence of eighteen rod-shaped chromo- 

 somes in the male pig and 20 in the female. 

 Two of the chromosomes in the male cells 

 usually stand apart from the other. They re- 

 main very conspicuous throughout the ripen- 

 ing stages and in the first division stand quite 

 aloof from their neighbors, passing undivided 

 to the "female daughter cell." In the second 

 ripening division they divide as other chromo- 

 somes, giving eight for one cell and 10 (8 

 common and 2 sex-chromosomes) for the 

 other. The common chromosomes fuse at 

 this point as in man, to form half the number 

 of double elements, but this has no effect 

 upon the final result. If the cell with eight 

 meets a female cell, all of which have 10 

 after ripening, the result would be a male 

 pig, while if the cell with the two female 

 producing chromosomes meets a female cell 

 the result would be a pig with 20 chromo- 

 somes, which is to say, a female. It is inter- 

 esting to note that in the pig and many 

 other forms the mature spermatozoa are of 

 two distinct sizes, representing the two sexes, 

 — the female-producing being the larger, due 

 to the presence of the two extra chromo- 

 somes. 



Except from the standpoint of the number 

 of chromosomes, the method of sperm for- 

 mation in the horse is almost identical with 

 that of the pig. In the horse there is only 

 one female determining chromosome, which 

 behaves as the two in the pig. The number 

 in the green cells of the stallion is 37, rep- 

 resenting two types of sperms with 18 (9 

 double) and 19 (9 double, 1 single) chromo- 

 somes, respectively. According to these fig- 

 ures, the mare which has never been exam- 

 ined, should possess 38 chromosomes. 



Further consideration might be given to the 

 general methods of sperm formations in oth- 

 er mammals, as the cells of the cat, squirrel, 

 rabbit, white mouse, bull, dog, guinea-pig, rat, 

 opossum and bat have been, or are being 

 studied. The above discussion, hov/ever, will 



suffice to show the general process involved 

 in the sperm formation of the normal ani- 

 mals. 



XT. Cause of Sterility of the Mule. In 

 conclusion I wish to call attention to a case 

 of cell study which is attracting the atten- 

 tion of many classes of people, from the se- 

 cluded cytologist to the most practical farmer. 

 The cause of the sterility in the common 

 mule is especially interesting since it is a 

 well known fact that this animal possesses 

 the necessary organs and a passion similar 

 to that of the horse or ass. A study of the 

 early cells of the testis of this animal shows 

 normal cells with 50 ordinary chromosomes 

 and one sex-determiner. It will be remem- 

 bered that the horse has only 36 plus the 

 extra chromosome. "This suggests that the 

 number in the ass is about 65, thus making 

 a difference of about 28 chromosomes be- 

 tween the parents of the hybrid." With such 

 marked difference in the number of chromo- 

 somes in the parents, one would expect a 

 catastrophe somewhere along the line of cel- 

 lular development. Indeed, the germ cells do 

 meet with such a disaster while in the process 

 of ripening. (Figs. 4, 5, etc.) 



We have shown in other forms that the ma- 

 ternal and paternal chromosomes are not di- 

 rectly associated in the somatic and early 

 germ cells, but lie side by side, divide and 

 carry on their other necessary functions in- 

 dependently, though in the same cell. This 

 clearly accounts for the real existence of the 

 mule. Should these chromosomes not act in- 

 dependently, the conflict would occur at fer- 

 tilization and thus the mule would be an im- 

 possibility. This independent action further 

 permits the existence of the desired charac- 

 teristics of both horse and ass in one inter- 

 mediate individual, but does not explain the 

 possibility of an offspring from this hybrid. 



While considering the typical ripening 

 stage, it was noted that there is a pairing of 

 homologous chromosomes from father and 

 mother. "In case of the mule, however, be- 

 cause the ovum and sperm contributed such 

 unequal numbers of chromosomes, there are 

 many without a homologue with which to 

 mate, and even in case of homologues the 

 physiological incompatibility of the two plasms 

 renders the pairing difficult and incomplete, 

 or prevents it entirely." This disturbance is 

 sufficient to cause a destruction of the ripen- 

 ing germ cell. Wodsedalek (1916) insists that, 

 "Most of the cells disintegrate during the pro- 

 phase, especially during the period of synap- 

 sis (Figs. 4, 5 and 6.) Others meet their fate 

 in the metaphase of the early anaphase stage 

 (Fig. 7). The remaining few that survive 

 the anaphase succumb soon after, and no sec- 

 ondary spermatocytes (Figs. 8 and 9) nor 

 spermatids (Fig. 10) and consequently no 



