SPERMATOGENESIS OF THE PIG. 2J 



The behavior of the accessory chromosomes in the various 

 stages of the spermatogenesis of the pig further substantiates 

 the fact that two different kind of spermatozoa are produced in 

 mammals. Since the dimorphic condition of the spermatozoa 

 does exist, the question arose whether this dimorphism holds true 

 in the chromosome number of the male and female somatic cells. 

 With this in view I undertook an examination of sections of male 

 and female embryological material supplied me by Professor 

 B. M. Allen. A large number of these sections were studied 

 and although mitotic stages were not very abundant in any one 

 section, and the chromosomes were frequently bunched together 

 rendering a count impossible, nevertheless, a number of counts 

 of the chromosomes in the germinal and somatic cells of the two 

 sexes were recorded. It was again found that the spermatogonial 

 number of chromosomes is eighteen, and that the same number 

 prevails in the somatic cells found in the mesonephros of the male 

 embryos. Two of the chromosomes are usually somewhat larger 

 (Fig. 59). Sections of the female material revealed a count of 

 twenty chromosomes in the oogonia (Fig. 60), and the same 

 number prevails in the somatic cells found in the mesonephros 

 of the female embryos (Fig. 62). Four large chromosomes corre- 

 sponding to the two accessories in the male can usually be de- 

 tected in the oogonial cells. In the somatic cells of the female 

 there are also four large chromosomes present corresponding to 

 the two accessories in the male cells and the four accessories in 

 the oogonia (Fig. 62). 



In a few cases ten large chromosomes were found in the early 

 metaphases of division in the somatic cells of the female (Fig. 

 61). Two of these are considerably larger and are interpreted 

 as the result of the pairing of the four accessories. The smaller 

 chromosomes, eight in number, judging by their size, are evidently 

 due to the pairing of the sixteen other chromosomes. The 

 position of these cells would not warrant the supposition that 

 they might be wandering germ cells. Furthermore, a similar 

 condition was not observed among the oogonial cells in spite of 

 the fact that mitotic stages occur far more frequently in the 

 sections of the ovaries than they do in the mesonephros. 



In proportion to the large number of mitotic stages found in 



