2OO EVIS HOWARD BERRY. 



half). In the lower cell the eleven ordinary chromosomes can be 

 counted. Resulting from the division of each primary sperma- 

 tocyte are two types of secondary spermatocytes, one containing 

 twelve chromosomes, and one eleven. These two types divide, 

 giving polar metaphase groups that show either twelve or eleven 

 chromosomes (cf. Fig. 3, d and g with eleven, and e and k with 

 twelve chromosomes). 



In side view the second division spindles are all of exactly the 

 same type (Fig. 3, a and b}. I have studied a great many of 

 them, and in no case do I find the odd chromosome passing un- 

 divided to one pole as Miss Wallace describes for Agalcna. 1 



As I have suggested before, the second division is an equation- 

 division, and the odd chromosome divides, in all probability, 

 along its original split, thus being distributed equally to each of 

 the resulting spermatids. The telophase, Fig. 3, /, represents 

 two of the early spermatids derived from the preceding type of 

 division, the odd chromosome still recognizable by its definite 

 shape and deep-staining reaction. From the division of the other 

 type of spermatocyte Fig. 3, / (without the odd chromosome), 

 are derived two spermatids without this dark nucleolus. There 

 are, therefore, two types of spermatids existing in equal num- 

 bers, one half with the odd chromosome, and one half without. 

 To establish this point, I counted in forty-four different fields, 

 all of the early spermatids with the odd chromosome, and all of 

 those without. This count gave a total of 287 of the former 

 and 286 of the latter, thus giving very positive evidence that the 

 two types of spermatids exist in the proportion of half to half. 



SUMMARY. 



1. The spermatogonia contain twenty-three chromosomes, 

 twenty-two ordinary ones and the odd chromosome. 



2. The odd chromosome is the chromosome-nucleolus of the 

 growth period. 



3. In the first maturation-division the odd-chromosome passes 



1 It seems possible that Miss Wallace may have mistaken a first division spindle 

 for a second-division. Her two types of second-division spindles, Figs. 27 and 28, 

 Plate IX., vary considerably in size, and by comparison of the larger, Fig. 28 (the 

 one with the accessory chromosomes), with Fig. 18, it could, 1 think, easily repre- 

 sent a first division. 



