16 GEORGE T. HARGITT 



4. SUMMARY 



In female colonies of Eudendrium egg cells appear to be widely 

 distributed, but careful examination demonstrates their pres- 

 ence only in the smaller branches. They are always in groups 

 located near the gonophores or in regions where gonophores 

 would have formed in the living colonies. The egg cells originate 

 in such positions, probably by modification of ectoderm cells, 

 but they pass into the entoderm, where early growth takes 

 place. The location of the eggs in the gonophores is due in 

 part, probably, to an active migration and in part to a passive 

 translocation caused by the growth of the tissues which go to 

 form the gonophore. An escape of nuclear material, probably of 

 chromatic nature, into the cytoplasm is coincident with the onset 

 of the growth period in the egg. In the male colonies sperm 

 cells arise in the deeper portion of the stems adjacent to, or in 

 the region of later formation of, gonophores. 



The germ cells of Eudendrium have commonly been discussed 

 as arising very early in the history of the hydroid from a dis- 

 tinct germinal tissue, and much later, at the time of maturity, 

 migrating into the reproductive bodies which are conceived as 

 degenerate medusoid buds. Observations do not substantiate 

 any of these interpretations, since the germ cells arise from 

 ectoderm or entoderm cells just previous to the development of 

 the gonophores, and the gonoptiores are not degenerate medusae, 

 but, in female colonies at least, develop by a modification of 

 ordinary polyps. There is no apparent phylogenetic signifi- 

 cance in the manner, place, or time of formation of the germ 

 cells of Eudendrium. 



