288 FERNANDUS PAYNE 



vations on material collected at Naples, Italy, and Freiburg i. B., 

 Germany. 



Briefly stated, the results formerly published are as follows: 

 There are 24 chromosomes in the oogonial cells and 23 in the 

 spermatogonial. Of the 23 one is noticeably smaller than any 

 of the others and smaller than any in the oogonial group. In 

 the first spermatocyte division there are 12 chromosomes. If 

 these chromosomes are studied in side view, 10 are found to be 

 bivalent and dumb-bell shaped, with the two parts of the dumb- 

 bell equal in size. Of the two others, one varies much in shape, 

 due in part perhaps, to the position in which it happens to lie. 

 It usually occurs to one side of the metaphase plate and may 

 have reached one pole of the spindle before the other chromo- 

 somes divide. It does not divide in this division. The second 

 of these two chromosomes is an unequal pair which divides 

 unequally. The large part of the unequal pair and the single 

 chromosome always pass in the first maturation division to the 

 same pole of the spindle. This causes two classes of secondary 

 spermatocytes, one with 11 chromosomes and one with 12. 

 They differ not only in number, but also in that the 11-class 

 gets the small end of the unequal pair, while the 12-class gets 

 the larger. All of the chromosomes divide in the second sper- 

 matocyte division, hence two kinds of spermatozoa are produced, 

 differing as did the secondary spermatocytes. As there are 24 

 chromosomes in the female and 23 in the male, the 12-class of 

 spermatozoa is female producing, the 11-class male producing. 

 My present observations confirm, without exception, the earlier 

 ones. At that time the count of the oogonial number (24) was 

 made in only one individual. I now have counts in three indi- 

 viduals (fig. 1, A, B, C), and each one shows clearly 24 chromo- 

 somes. I should like to have made counts in more individuals, 

 but the number of dividing cells in the ovary is very small and 

 many ovaries show none. The young testes, however, show 

 many, and here the number (23) has been counted in 12 indi- 

 viduals. In each case a small chromosome is present (fig. 1, 

 D to J). No two of the spermatogonial groups are from the 

 same male and hence are drawn from different slides. This 



