66 bulletin: museum of cuMPAKAnvE zoology. 



ing the cliaracteristic coloring to the bodies of the females in the 

 breeding season. ArnpMporus tigrinus has olive green ova, so that 

 the ripe females are banded with green. 



In the hermaphroditic Tetrdstemma caecwn the ova are fully two 

 thirds the diameter of the body itself, and hence a single ovum 

 develops in each of the ovaries, which are situated at intervals in a 

 single irregular row (PI. 22, fig. 151). The sperraaries are much 

 more numerous than the ovaries between which they are placed. 

 The speimaries usually develop first, and after the discharge of the 

 spermatozoa the ovaries become mature, but in some individuals the 

 process is apparently reversed. 



In Geonemertes agricola^ which is both hermaphroditic and vivip- 

 arous, some of the gonads produce ova only or spermatozoa only, 

 while in other gonads both kinds of sexual products may be formed 

 (Coe, : 04") . In the latter case the spermatozoa are matured first, 

 and after their discharge the ova develop, very much in the man- 

 ner described by Montgomery ('95) for Stichostemma. Each 

 ovary matures normally but a single ovum, although in the early 

 stages of its development all of the cells of the young gonad seem 

 to be exactly alike in size and appearance. In a short time, how- 

 ever, the cells become differentiated into three classes — young ova, 

 yolk cells and follicular cells. The latter form a thin layer about the 

 wall of the gonad and furnish the cells which form the duct by which 

 the sexual gland is connected with the exterior of the body. This 

 duct is formed comparatively early, and penetrates quite to the exte- 

 rior before the egg in the gonad has reached maturity. The yolk 

 cells are apparently merely egg cells which for some reason become 

 aborted at an early period. They are rather numerous in each 

 young ovary, and grow to a size several times that of the largest 

 follicular cells. They become crowded with yolk granules and 

 pressed closely against the wall of the developing ovum. To all 

 appearances the cell membranes separating ovum and yolk cells 

 break down and the latter are absorbed directly into the substance 

 of the ovum. The whole substance — cytoplasm, yolk, and nucleus 

 — of the yolk cell seems to be thus absorbed. There may be sev- 

 eral large cells in the young ovary which are distinguished from 

 the yolk cells by a more homogeneous cj'toplasm. These cells 

 increase rapidly in size and take on the appearance of young ova. 

 Eventually, however, all save one, or rarely two, cease their growth 



