IQO 



McCLUNG. 



[Vol. II. 



commences to shorten and grows into the form of a horseshoe, 

 and is finally to be distinguished from the chromatic rings only 

 by its deeper staining quality and by the smoothness of its 

 outline (Fig. lo). In the formation of the mitotic figure of the 

 first spermatocyte division, it assumes its position on the outside 

 of the group of chromosomes as it did in the spermatogonial 

 division, and again has the boomerang shape that marked its 

 appearance in the early figures (Fig. 1 1). When the chromatin 



Fig. g. — A somewhat later spermatocyte 

 prophase. The accessory chromosome 

 viewed from the side. 



Fig. id. — " Ring " stage of the spermatocyte. 

 The accessory chromosome distinguishable 

 from the remaining nuclear elements by 

 reason of its greater density and smoother 

 outline. 



Fig. u. — Metaphase of the spermatocyte. 

 The accessory chromosome in the shape 

 of a boomerang at one side of the group 

 of. chromosomes. 



Fig. 12. — I^ate anaphase of tlie sperma- 

 tocyte. The accessory chromosomes in 

 the form of double horseshoes in the 

 two daughter-cells. 



separates and moves to the two poles, the accessory chromosome 

 divides longitudinally and presents the appearance of two horse- 

 shoes with their rounded ends in contact (Fig. 12). In the 

 second spermatocyte division, apparently the same process is 

 followed. 



The recently formed spermatids possess a nucleus in which 

 the ordinary chromatin is extremely scant (Fig. 13) and very 

 weak in staining power, while the accessory chromosome shows 

 as prominently as ever and stains in the same uniform manner. 

 It is not easy to trace out the part that the different elements 



