102 NICHOLS — SPERMATOGENTESIS ONISCUS ASELLUS LINN. [April 4, 



plasm in Astacus. This body, however, seems not to be affected 

 by mitosis, but lies passively to one side. In the vicinity of the 

 poles are, however, numerous granules (''corpuscles polaires") (Fig. 

 246/, PL VII). The " Nebenkern" of Crangon, according to the 

 description, behaves like the substance designated idiozome by 

 Meves. The "corpuscles polaires" of Astacus may be of a similar 

 nature. For the other forms studied no bodies of any kind lying 

 in the cytoplasm are shown. The substance seems to be unusually 

 prominent in Crangon and Astacus, The cells of both are of large 

 size. 



1 89 1, vom Rath settled the question of amitotic division of the 

 germ cells of Astacus in the negative. He states that a minority of 

 the spermatogonia undergo no change at first, but give rise by 

 mitosis to new spermatogonia after the discharge of the ripe sper- 

 matozoa. He mentions a case of regeneration of an entire follicle 

 from a single spermatogonium. With the first appearance of the 

 spermatids the follicle cells (''Randkerne") commence to grow in 

 size and divide amitotically. The direct division apparently takes 

 place by a sharp breaking apart of the portions of the nuclei, re- 

 sembling a slicing. Degeneration of the nuclei follows. At the 

 point of transition between follicle and duct there is often an extra- 

 ordinary growth of cells by amitosis. The results of his research 

 are interpreted by vom Rath to mean that two kinds of cells have 

 arisen from indifferent epithelium, one dividing mitotically, the 

 other amitotically. 



Is op o da. 



1884. Gilson states that it is only at certain seasons of the year 

 that the spermatogenesis of these animals can be studied with 

 profit. In the case of Oniscus asellus, from July to November is 

 the most favorable season for obtaining preparation of what he 

 calls the first stage ("premiere etape"). In the case of Asellus 

 aquaticus it is later — about the month of February. 



Oniscus asellus. — The cells filling the apical end of the caeca 

 (spermatogonia) are mentioned, and the opinion is expressed that 

 they constitute a reserve mass destined to replace by proliferation 

 the elements organized in the lower part of the tube and later 

 evacuated. Karyokinesis in these cells (spermatogonia) was ob- 

 served but once, and the stages intervening between them and the 

 spermatocytes were not discovered. 



