SMALLWOOD. — POLYCERELLA ZOOBOTRYON. G19 



and nidamental glands and is more conspicuous on the left side. The 

 posterior genital mass projects forward over the dorsal aspect of the 

 anterior genital mass, concealing about one half of it as seen from above. 

 Into the genital atrium open the oviduct and receptaculum seminis 

 close to each other and also the penis sac. The detailed relation of 

 each duct to the posterior and anterior genital masses and to the 

 genital trium is presented in the following paragraphs. 



Posterior Genital Mass. 



In the posterior genital mass the arrangement of the male and fe- 

 male portions does not follow any definite plan ; the ultimate tissue 

 from which the germ cells are derived is a columnar epithelium com- 

 posed of short and broad cells. This epithelium is much folded, form- 

 ing follicles which project inward toward the center of the genital 

 mass. A cross section of the genital mass shows many knob-like re- 

 gions of eggs and sperms projecting almost to the center of the mass. 

 Between such projections the liver cells of the anterior region often 

 extend to the surface. Elsewhere in the anterior two thirds of this 

 genital mass the germinal follicles envelope the liver in a layer of 

 varying thickness. Each follicle is exclusively occupied by growing 

 eggs or sperm cells. 



The sperm cells in the material collected in January seem to be 

 mostly in a state of maturity, but the eggs exhibit all stages of devel- 

 opment. The maturing eggs show in a clear manner the relation of 

 the nucleus to the formation of deutoplasm. All stages from the 

 young ova to the mature egg are seen in the same section. In the 

 young ovum the cytoplasm is evenly and finely granular ; as it increases 

 in size, small spherical droplets appear in close contact with the nuclear 

 membrane ; as growth continues several rows of droplets are distin- 

 guishable surrounding the nucleus. In the more mature egg finger- 

 like masses of these droplets extend from the nucleus toward the 

 periphery of the cell; these continue to become more numerous until 

 the early finely granular condition is obliterated. In Hermann's fixa- 

 tion these deutoplasmic droplets are of all shades from a deep brown 

 to black, indicating that at least a considerable portion of their sub- 

 stance is of a fatty composition. Miiller's fixation followed by the usual 

 iron haematoxylin gives the best differentiation for the study of the 

 growth of the deutoplasm. 



The numerous follicles open into an irregular series of minute ducts, 

 which are finally collected into the common hermaphroditic duct. Be- 

 fore taking up the course of this duct, it is necessary to describe the 



