ISO L. B. WALLACE. 



We might here mention once more that the accessory chromo- 

 somes show a staining reaction throughout which the other 

 chromosomes show at the height of mitosis and which some 

 think to be due to the presence of a larger amount of nucleinic 

 acid at that time. Now while staining reactions are not a safe 

 criterion, they may give us at least a rough test of the chemical 

 conditions in a cell, and since the nuclei of spermatozoa have 

 been found to contain a maximum of nucleinic acid, and since 

 the " bevorzugten zellen " in the spider might be richer in nu- 

 cleinic acid, on account of the presence of the accessory chromo- 

 somes, than the remaining three fourths of the male germ cells 

 which are not so favored, we might here see a new significance 

 in the accessory chromosomes. 



SPERMATIDS AND SPERMATOZOA. 



A study of the spermatids will throw further light upon the 

 subject of the distribution of the accessory chromosomes. In 

 most cases it is evident that when the secondary spermatocytes, 

 which do contain the accessory chromosomes, divide, the latter 

 pass to but one of the resultant spermatids (Plate II., Figs. 

 29-33). Figs. 34 and 35 show spermatocytes which are not 

 "favored cells." Sometimes each of the two spermatids result- 

 ing from the division of a favored spermatocyte seems to contain 

 one accessory chromosome, but I think this should be regarded 

 as an exceptional case (PI. II., Fig. 37). At a later stage in the 

 formation of the spermatozoon it is impossible to determine 

 which "cells contain the accessory chromosomes and which do 

 not. At the beginning of the process of the condensation of 

 the chromatin to form the head, the two accessory chromosomes 

 become closely applied to one another, then appear to fuse to- 

 gether. They still take the safranin stain and form a center into 

 which the chromatin reticulum which takes the violet stain, is 

 gradually drawn until all of the chromatin forms a compact mass 

 stained brilliant red. In the spermatids which lack the accessory 

 chromosomes the chromatin at one point in the reticulum forms 

 a net-knot which now takes the safranin stain and it becomes the 

 center of condensation and so simulates the appearance of the 

 favored cells. At such a stage one might be mislead into think- 



