64 J. F. McCLENDON. 



cells lie just beneath the ectoderm until the Metanauplius stage, 

 when by concentration of the ventral nerve chain, the latter is 

 pushed under them and they rest on top of it (Fig. 56). I have 

 said the germ cells have large nuclei --the nucleus is further 

 characterized by the fact that the chromosomes remain distinct 

 as oval masses just inside the nuclear membrane (Fig. 52). The 

 chromosomes can be counted and are sixteen, just twice the 

 number in the female pronucleus. The cytoplasm is much 

 vacuolated. The germ cells are flattened against each other, 

 and are flattened against the ectoderm in the early stages (Figs. 

 49, 50). In later stages they detach from the ectoderm, and 

 round up (Figs. 52, 56). And still later (during the Metanau- 

 plius stage from 24 to 72 hours after hatching of the larva) they 

 separate and pass laterally and upwards into the yolk and two 

 of them come together dorsal to the intestine, and I have not 

 traced them further than the fourth day after the larva hatched, 

 when they were still two in number. Pedaschenko says that two 

 of the four genital cells pass to the right and two (one lateral and 

 one median) to the left. Each pair fuse and, probably by degen- 

 eration of one nucleus, becomes a single cell, which finds its way 

 upwards and posteriorly and by division forms the ovary of that 

 side. The fusion of each pair he considers of great significance 

 and the basis of a theory on the origin of the sex of the adult. 

 He believes that one cell of each pair is male and one female and 

 the one whose nucleus persists after fusion of the cytoplasm de- 

 termines the sex of the animal. His belief that two cells of the 

 four are male and two female is based on comparison with O. 

 Hertwig's account of Sagitta in which this condition exists, with 

 difference however in the later history. In Sagitta the two 

 female cells give rise to the ovaries (in the anterior part of the 

 animal) and the two male cells give rise to the testes (in the pos- 

 terior part of the animal). 



Sex is said to be determined in some animals by amount of 

 food (of the individual, the parents, or the grandparents) in others 

 by fertilization vs. parthenogenesis, in others by dimorphism of 

 egg or spermatozoon, in others by temperature, etc. Peda- 

 schenko proposes an additional factor. 



Haecker ('97) found in Cyclops the primary germ cell differen- 



