Nos. 451-452.] AMERICAN SOCIETY OF ZOOLOGISTS. 507 



is too well developed to allow of such an explanation anc 

 it divides in the second maturation division only and i 

 distributed to but one-half of the spermatids, he regards 

 sex-determinant. 



In the spider A^-alena ncevia, the peculiar chromosome < 

 resembles the one described by McClung and tlicrctore I 

 his term but my results differ from his in regard to its di 

 tion. I am convinced that, although si)lit longitiidin: 

 takes part in neither of the maturation divisions and that, 

 fore, only ont-fourth of the resulting spermatids posses 

 Such a condition would hardly favor the idea of sc\ clelci nn 

 Figures i, 2 and 3 show spermatocytes of the first mati 

 division and Figures 4, 5 and 6, spermatocytes of the 



, of maturing spermatozoa ; 



degeneration (Fig. 7) and these occur in great numbers m \ 

 testis and also in the ducts (Fig. 8) together with the mi 

 smaller number of ripe spermatozoa. This fact leads me 

 suggest that possibly only those spermatids which contain 1 

 accessory chromosome develop into functional spermatozoa z 

 that the remaining three-fourths never reach maturity. If t 

 I parallelism could be drawn betw( 



interpretation be a 1 

 the development of the spermato; 

 the latter only one of the four ootids develops 



of the ( 



