308 Elliot E. Downing, 



3. Only a single eg-g (or very rarely two) is produced in one 

 ovary in H. viridis, H. fusca and H. grisea-^ in H. dioecia, several. 

 The large ovaries of this last species contain at the beginning several 

 eggs, produced by the division of one of the early oogonia or even 

 of an egg that has already achieved some initial growth. Division 

 stages of such eggs have not infrequently been observed; some are 

 shown in Fig. 2, Plate 11. 



4. The ovary is formed by a rapid multiplication of the inter- 

 stitial cells about the egg or eggs at the site of the ovary. This 

 multiplication is by mitosis, twelve chromosomes appearing in the 

 figure. 



5. There is no evidence of a migration of the interstitial cells 

 to the ovary. Kleinenbeeg says that the interstitials are relatively 

 infrequent about the ovary and on the basis of this supposed fact 

 he thinks that their accumulation may be in part due to migration 

 although he has no direct evidence of such migration. Nüssbaum 

 pointed out that if infrequent the interstitials were still present 

 about the ovary in sufficient numbers to permit of the formation of 

 new ovaries, of testes and of buds in the immediately adjacent 

 territory. I am quite confident that the interstitials are as common 

 immediately about an ovary as elsewhere on the body in H. fusca 

 and H. dioecia: this has been determined by counting the number of 

 such cells in equal areas at varying distances from the oyhyj in 

 sections of many individuals. A similar result was reached by the 

 same method in the study of the spermatogenesis of the hydra. 

 Such active movement of the germ cells is much less common than 

 formerly thought; many apparent instances are entirely discredited. 

 GoETTE, after extensive studies, concludes that there is little or no 

 evidence for such active, instinctive wanderings of the germ cells in 

 the hj'droids; such movements, when they do occur at all, are largely 

 passive. He says: "Die Wanderung der Keimzellen der Hydropolypen 

 vollzieht sich entweder passiv durch die Wachstumsbewegung des 

 sie enthaltenden Ectoderms oder Endoderms, oder nur teilweise 

 aktiv, wobei sie jedoch durch die Formbedingungen dirigiert wird, 

 die in den umgebenden Teilen enthalten sind. Für die Annahme 

 eines die Wanderung i-egelnden und richtenden Instinkts der Keim- 

 zellen fehlt jede Veranlassung" (p. 298). 



6. The interstitial cells begin to multiply at several points, 

 forming small independent masses adjacent to the eggs: these 

 separate masses fuse as continued growth crowds them together. 



