296 bulletin: museum of comparative zoology. 



cytoplasm is coarsely alveolar (Figs. 3-11), and frequently encloses 

 spherical masses, probably of metaplastic nature, which osmosize more 

 strongly than the ordinary protoplasm, are not easily dissolved by either 

 acids or alkalis, and no doubt correspond in their nature to the bodies 

 of similar appearance found in the germ cells of both sexes. There are 

 likewise frequently present in the cytoplasm clusters of the small brown 

 pigment granules which give to the gonads of Gonionemus their char- 

 acteristic color. No archoplasmic structures of any kind are to be seen 

 except during active mitosis, nor can a centrosome be detected with any 

 certainty, although occasionally a minute granule is to be found, which 

 may perhaps represent that structure. The nucleus, during the " rest- 

 ing " stage, is approximately spherical and measures only 5.5 ft in diameter, 

 so that it is decidedly smaller than in the spermatogonia (page 302), and 

 agrees closely in size with the nuclei of oogonia and of the ectodermal 

 covering cells of the gonad. As a rule, it encloses a single very large 

 nucleolus, but occasionally two or three are present, all of noi-mal struct- 

 ure, though of rather less than normal size. The nucleolus when stained 

 with iron haematoxylin shows in most cases a dark peripheral ring or 

 shell, enclosing a pale or even transparent central mass (Fig. 3) exactly 

 as is seen in the nucleolus in the spermatogonia (page 302). The deeply 

 staining shell, as we shall see from its later history, is probably composed 

 of chromatin, while the central sphere is to be regarded as corre- 

 sponding in nature to a plasmosome. This type of compound nucleolus is 

 characteristic of all the adult somatic cells of Gonionemus thus far ex- 

 amined, as well as of both spermatogonia and oogonia. The nucleus is 

 rilled by a mass of dense, granular karyoplasm, which stains readily with 

 plasma dyes, and through it runs a delicate achromatic reticulum, radiat- 

 ing from the nucleolus (Fig. 3) and bearing at its nodes a large number 

 of small thickenings or karyosomes. The nuclear membrane is thick, 

 stains darkly, and is apparently of granular nature. "When treated 

 with the Auerbach mixture of acid fuchsin and basic methyl green, the 

 cytoplasm, nuclear membrane, karyoplasm, reticulum, and karyosomes 

 select the red, acid dye ; the outer shell of the nucleolus alone selecting 

 the basic dye, while its central plasmosome usually appears of a dull 

 brownish tint. The nucleolar shell thus presents the acid reaction typi- 

 cal of chromatin in mitosis, while all other portions of the cell are now 

 basic in this respect. 



The first change in the prophase is a thickening of the threads of the 

 reticulum and an increase in the size and staining capacity of the karyo- 

 somes (Fig. 4). The karyoplasm now loses its granular appearance aad 



