WILCOX: SPEKMATOGENESIS. 27 



POSTSCRIPT. 



In the Bulletin of the College of Agriculture of the Imperial Univer- 

 sity of Japan has recently appeared a paper by Kametaro Toyama ('94), 

 " On the Spermatogenesis of the Silkworm." The author has arrived 

 at conclusions which in part agree with my own, but in part are cpiite 

 different. 



Like myself, Toyama was unable to find any longitudinal splitting of 

 the chromatic thread in the prophases of the first spermatocyte division. 

 He gives the following account of the complicated series of movements 

 of the chi'omatin during the prophases : " A nucleolus is generally seen 

 in the network of linin and chromatin. . . . Most of the chromatin 

 granules become collected to one side of the nucleus and form an irreg- 

 ular mass, . . . become again separate from each other and arrange 

 themselves along the radiating linin fibres, and the skein stage is thus 

 obtained, . . . The chromatin granules scattered in the nucleus 

 become again collected in the centre of it, and present an irregular mass 

 as before. ... In a still later stage the chromatin granules again 

 commence to separate from one another. ... A little before the 

 appearance of the centrosomes in sperm-mother-cells the chromatin 

 granules . . . gradually collect here and there and assume ring-shaped 

 structures." 



Unfortunately the author presents no satisfactory evidence for this 

 series of changes. He may have seen all the stages which are enumer- 

 ated above, but he gives no proof that they succeed one another in the 

 order he has stated. In the earliest prophases Toyama finds the chro- 

 matin in nearly the same condition in which T find it in Caloptenus, and 

 just before the first maturation division he finds the chromatin an-anged 

 in quadrivalent rings. The progress toward the ring stage is, according 

 to his account, twice interrupted by retrogressive processes. One can- 

 not easily conceive the purpose of these complications, and the evidence 

 for such an hypothesis could never be conclusive without direct observa- 

 tion of the process in the living condition. I know no reason why we 

 might not arrange Toyama's Figures 23-43 in one continuous series. 

 All stages represented in those figures are very young, and the numerous 

 intermediate stages between them and Figure 44 are not shown. The 

 concentrated condition of the chromatin seen in the author's Figure 30 

 seems to me due to bad preservation. 



I disagree entirely with Toyama as to the processes in the maturation 



