312 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



the secondary spermatocytes, spermatids, and spermatozoa constitute the 

 outermost layer (Fig. 2, which shows a cross section of a gonad). 



The so-called resting stage of the cells under consideration appears to 

 persist for a considerable period, since cells in this condition are very 

 abundant ; but there is little or no growth connected with it ; in this it 

 differs markedly from the corresponding phases of both the spermato- 

 gonia and the female germ cells of Gonionemus, as well as from the con- 

 ditions of the cell generations so commonly described by other authors 

 among higher Metazoa, particularly arthropods (cf. especially Black- 

 man, : 05). 



The nucleus (Plate 3, Fig. 40) is oval; its membrane, which is dis- 

 tinct and granular, stains strongly with acid dyes ; the karyoplasm is 

 dense ; the achromatic reticulum, many of whose strands take their origin 

 in the substance of the nucleolus, is very delicate and bears at its nodes 

 small thickenings, the karyosomes. I have been able to make a more 

 thorough study of the karyoplasm in this than in the other cell genera- 

 tions, particularly in crushed preparations, and with the following re- 

 sults. As far as its chemical reactions are concerned, it stains but 

 slightly, even after prolonged chlorine bleaching, and then only with 

 acid dyes, not at all with basic ones, presenting in this a sharp contrast 

 to the corresponding substance in the oocytes, which with the same 

 treatment show a very strong affinity for plasma stains. After treatment 

 with osmic acid it forms a solid and very brittle mass, which, when forci- 

 bly extruded from the nucleus, breaks into angular and irregular frag- 

 ments, presenting a characteristic granular appearance very different 

 from the reticulate cytoplasm surrounding it. Finally, after treatment 

 with Flemming's fluid, it is, at this stage, of a peculiar yellowish color seen 

 in no other part of the cell. Since there is little doubt, from its previous 

 history, that it is derived from ordinary cytoplasm, we must suppose 

 that it has undergone these modifications under the influence of the 

 metabolic processes of the nuclear structures. 



The nucleolus is much smaller, both actually and in proportion to the 

 size of the cell, than in resting spermatogonia (cf. Figs. 40 and 41 with 

 Figs. 15 and 16), and, as shown by its origin and fate, is a purely chro- 

 matin structure, a feature previously noted by Guenther (:04) in sperma- 

 tocytes of Hydra viridis. It is, as previously noted, a precise criterion for 

 distinguishing cells of these two generations. Usually it is single ; occa- 

 sionally, however (Fig. 41), there are two, both of normal size, in which 

 case each acts in the prophase independently of the other. The cytoplasm 

 when compared with that of spermatogonia is rather scanty, and presents 



