470 M. Louise Nichols. 



during the median stages of its development loses considerably in 

 staining power, it never becomes so pale as in the spermatid of 

 Hippa.' (PL 2. O, 4-5.) 



In the young dpermatid of the Amphipod Talorchestia a small, 

 spherical '"Nebenkem" may be seen. This enlarges and elongates 

 as the rest of the cytoplasm diminishes. Finally a differentiation 

 is brought about into middle-piece and tail. (PI. 2. T, 15-18.) 

 I have no stages showing a temporary loss of staining power in the 

 nucleus, and do not, therefore, know whether this occurs in Talor- 

 chestia, or whether the nucleus shown in Fig. 15 is a direct trans- 

 formation of the daughter nucleus of the second spermatocytic 

 division. 



Spekimatogenesis up to the Formation of the Spermatids. 



Spermatogonia. — The spermatogonia of the different forms are 

 sufficiently unlike to permit of their being recognized without diffi- 

 culty. The unlikeness is referable chiefly to the size of the nucleus 

 itself, to the number, size, position and shape of the nucleoli, and to 

 the manner in which the chromosomes arise. 



The spermatogonia of the Isopoda resemble each other more closely 

 than they do that of the Amphipod; also the spermatogonia of the 

 Decapoda bear more resemblance to each other than they do to those 

 of the Amphipoda and Isopoda. Again those of Homarus and 

 Astacus are more like each other than like Hippa. 



In Talorchestia the nucleolus is found close to the nuclear membrane 

 and is often irregular in sha]ie. jMore than one is freq\iently present. 

 (PI. 1. T, 1.) The nucleolus of the Isopoda has usually a slightly 

 eccentric location and in Idotea is considerably larger than in Onis- 

 cus, although the nucleus as a wdiole is larger in Oniscus. (Figs. 

 I, 1-2, 1.) In the Decapoda the nucleolus is usually central or 

 nearly so, and in all it consists of two substances staining in different 

 degrees of intensity with iron hsematoxylin. In Astacus and Homarus 

 the more deeply staining substance collects around a few centres, but 

 in Hippa it is irregularly distributed through the nucleolus. (PI. 1. 

 Hi, 1; Ho, 1; A, 1.) Of course the amount of granular material 

 varies in different nucleoli and appears more abundant in darkly 

 stained preparations. 



