6 bulletin: museum of comparative zoology. 



cases counterstaining with Congo red was of value. However, the 

 chief value of the latter stain was found in the work upon the meta- 

 morphosis of the spermatid, where it was nearly indispensable in study- 

 ing the early stages in the formation of the axial filament. For in 

 sections stained with haematoxylin alone the very young axial filament 

 could hardly be distinguished from the cytoplasm, bui, when Congo red 

 was used as a counter stain, the cytoplasm in well-decolorized sections 

 was stained orange-red and thus served as an excellent background 

 for the black filament. I believe that the value of Congo red as a coun- 

 ter stain for haematoxylin, when used after Gilson's fluid or other sub- 

 limate-acetic mixture in the study of the spermatid changes, can hardly 

 be overrated. 



III. Observations. 

 1. Introductory. 



In studying the spermatogenesis of Scolopendra one is surprised at 

 the striking similarity of the cells in their general appearance and in 

 their behavior to those of the female germ elements of various animals. 

 Indeed, it is often the case that, were the cells isolated and mounted by 

 themselves, they would be immediately and invariably mistaken for 

 stages in oogenesis. This resemblance is most striking in the stages 

 beginning immediately before the prophase of the first spermatocyte and 

 extending to the completion of the second spermatocyte, but it is also 

 very pronounced even in the earlier phases. 



After the completion of the "division period" the cells, which are at 

 that time very small, immediately begin to increase rapidly in size. 

 They continue to grow until finally, when they are ready for the matu- 

 ration divisions, their bulk is many times that of the spermatogonium. 

 This enormous growth suggests of itself a comparison of the spermato- 

 cytes of Scolopendra with egg cells. But there is also a surprising 

 similarity in the structure of the cells themselves as well as in their 

 general appearance. By the time the two cells arising from the last 

 spermatogonial division are really separated by a membrane and the 

 nucleus has been reconstructed, the cytosome has already increased con- 

 siderably in size. The chromatin at this stage, as in eggs, is in the form 

 of a number of granular segments distributed irregularly throughout the 

 nuclear space, and upon one side of the nucleus, in close contact with 

 the membrane, there is a chromatin body which in general shape re- 

 sembles the karyosomes often seen in growing eggs. In later stages the 



