NEW TYPES OF CHROMOSOME DISTRIBUTION. 14! 



Fifteen of the 20 take up the position of a ring, within which is 

 a definite compound element formed by the remaining five. 

 These are now arranged in a pentad group, which always shows 

 the same composition and occupies the same position. Four of 

 these five chromosomes are grouped very closely together and lie 

 in one plane, while the other one is either above or below this 

 group of four, lying close to them on the other side of the 

 equatorial plane (Fig. 8, A, polar view of the equatorial plate; 

 Fig. 8, E, and Fig. 9, C, side views). The 15 chromosomes in 

 the ring divide equally, while the chromosomes of the central 

 pentad do not divide individually, but the group as a whole sepa- 

 rates in such a manner that one chromosome passes to one pole 

 and the other four to the other pole (Fig. 8, F, and Fig. 9, D 

 and F). Two classes of spermatozoa are thus formed, which 

 contain 16 and 19 chromosomes respectively. The early anaphase 

 illustrating these two -classes is shown in Fig. 8, G, H and 7, and 

 Fig. 9, B ; the later anaphase in Fig. 8, C and D." 



In my previous paper, I also stated somewhat cautiously that 

 35 was the number of chromosomes in the spermatogonia, as the 

 count was made in only two cells. Fig. 7, C and D, shows two 

 new groups and I have counted the chromosomes in several other 

 cells, each case showing the same number. At present, I have, 

 therefore, no hesitation is saying that 35 is the number of chromo- 

 somes found in the male cells. The female number (oogonial 

 or follicle cells) is 38 (Fig. 7, A and B}. From these facts it is 

 evident that the reduced female group must contain 19 chromo- 

 somes ; and that accordingly females are produced upon fertiliza- 

 tion by the ig-chromosome class of spermatozoa; males upon 

 fertilization by the i6-chromosome class. 



Egg 19 plus spermatozoon 16 = ^35 



Egg 19 plus spermatozoon 19 = 38 (5). 



During the growth period, between synapsis and the formation 

 of the chromosomes preparatory to the first spermatocyte divi- 

 sion, a large deeply staining body persists, which is more or less 

 comparable to the nucleolus of the forms previously described. 

 In the preliminary note, I suggested the possibility that this body 



