304 bulletin: museum of comparative zoology. 



Although the cytoplasm does not exhibit any archoplasmic structures, 

 it does, in the case at least of the larger cells, contain a greater or less 

 number of deeply staining masses which are of various sizes, homoge- 

 neous structure, indefinite outline, and lie as a rule close to the nuclear 

 membrane (Plate 2, Figs. 15, 17, 24, 27). These bodies blacken with 

 osmic acid, and after being bleached with chlorine combine strongly 

 with acid dyes. In appearance and general structure they are evidently 

 closely allied to certain structures found in the younger oocytes of the 

 same species (see page 341 and Plate 5, Figs. 109, 115; Plate 6, Fig. 

 125), and to some of the various metaplasmic objects in other eggs which, 

 in spite of their diverse natures, have been grouped together under the 

 name of yolk nuclei. Although these structures first appear in con- 

 tact with the nuclear membrane (Fig. 1), there is no evidence that they 

 are actually nuclear products. But we must, I think, conclude with 

 Crampton ('99), and E. B. Wilson ( : 00) that they are of cytoplasmic 

 origin, formed, however, under the influence of the metabolic activity 

 of the nucleus. Eventually, during the prophase of the last spermato- 

 gonial mitosis, they gradually dwindle and disappear. 



The staining reactions, which afford the best available index to the 

 chemical conditions of the different cell structures, are of interest. In 

 the resting spermatogonia, after treatment with the Auerbach mixture, 

 cytoplasm, metaplasm, nuclear membrane, karyoplasm, karyosomes, linin 

 reticulum, and sometimes the central portion of the nucleolus, select the 

 acid (red) dye, the only nuclear structure selecting the basic dye being 

 the nucleolar " shell." I do not, however, believe that this is conclusive 

 evidence that this shell now contains all the chromatin which is later 

 visible, since the later stages show beyond doubt that the karyosomes 

 contribute to it. 



Prophase. — At the close of the growth period the cells enter upon 

 the prophase of the last spermatogonial mitosis. In general this resem- 

 bles the somatic mitosis already described ; yet differs in certain stages 

 of the prophase, especially in the mode of formation of the definitive 

 chromosomes. The first apparent change affects the achromatic network, 

 which becomes stouter, while the karyosomes lying at its nodes increase 

 in size and staining capacity without, however, as yet changing their 

 chemical reaction (Plate 2, Figs. 19, 20). It is now more evident than 

 in the resting stage that many of the achromatic strands radiate out- 

 ward from the nucleolus. The chromatic shell of the latter loses its 

 continuity and presents the appearance of numerous distinct masses, a 

 change which is contemporaneous with a marked increase in the stout- 



