IO Edmund B. Wilson 



but which particular one cannot be determined by simple inspec- 

 tion, since the three are of nearly equal size. In synapsis two 

 of these large chromosomes unite to form the largest of the ten 



O O 



bivalents (/, Fig. 2, a) that appear in the first spermatocyte 

 division. The third, which retains its compact form as a chro- 

 mosome-nucleus during the growth-period, remains as the univ- 

 alent heterotropic chromosome (h, Fig. 2, a). The first spermat- 

 ocyte division accordingly shows eleven chromosomes, ten of 

 which are bivalent, and one (heterotropic) is univalent. The 

 distribution of these chromosomes in the maturation-division takes 

 the usual course, the heterotropic chromosome dividing equally 

 with the ten bivalents in the first mitosis while its products pass 

 undivided to one pole of the spindle in the second (Fig. 2, 6). 

 Half the spermatozoa accordingly receive ten chromosomes, one 

 of which (/, Fig. 2, <:) is larger than the others, and half an exactly 

 similar group plus the large heterotropic chromosome, or eleven 

 in all (Fig. 2, J). 



The oogonial groups show invariably twenty-two chromosomes, 

 which may be arranged in eleven equal pairs (Fig. 2, g, h). In 

 place of the three large chromosomes of the spermatogonial 

 groups appear four similar chromosomes, forming two equal 

 pairs. Two of these four are obviously the large chromosome, 

 common to all the spermatozoa, and its maternal mate, while 

 the other two must be the heterotropic chromosome (derived in 

 fertilization from the spermatozoon) with its maternal mate. 

 It is, therefore, clear that all of the matured eggs must contain 

 eleven chromosomes, that females are produced upon fertilization 

 by those spermatozoa that contain a similar group /'. <?., by those 

 containing the heterotropic males upon fertilization by spermat- 

 ozoa that lack the heterotropic. 



The ovarian follicle-cells often show chromosome-groups 

 identical with those of the oogonia (Fig. 2, /). Not infrequently, 

 however, the number of chromosomes is much greater, and the 

 same is true of the nuclei of the investing cells of the ovary, of 

 the oviduct and of the fat-body. In the male similar multiple 

 groups are not uncommon in the interstitial and investing cells 

 of the testis. Only in a single case have I succeeded in gaining 



