300 Elliot R. Downing. 



hydra is bearing- sex organs it will generally not regenerate. This 

 fact favors the hypothesis that a condition of depression accompanies 

 the sexnal condition. 



The new evidence that I can oifer is, then, contradictor}' and 

 the whole question of the factors that determine the appearance of 

 the sex organs must be left open. Whether or not the nucleo- 

 plasma relation be the precise one, change of which will produce 

 the sexual condition, we are certainly indebted to E. Heetwig for 

 turning our attention toward an alteration of the relation of parts 

 of an organism as a determining cause rather than to some single 

 factor in the complex of the animal's environment. 



Proterogyny. 



Continued observations do not confirm my previous statements 

 that H. fusca is usually proterogynous. While in the observations 

 made up to the time of the published statement the animals were 

 found to produce eggs first, invariably, since then I have frequently 

 happened to have specimens that developed spermaries first. Kleinen- 

 BERG noted that the sexual activity begins, as a rule, with the 

 formation of the testes. D. D. Whitney finds that in H. viridis the 

 sperm appear first and E. Heutwig finds, in his experiments, a 

 large percentage of the sexually mature forms produced are males. 



Order of Appearance of the Ovaries. 



The ovaries (and testes) tend to appear in pairs opposite each 

 other. I can, as yet, find no evidence of such a succession of them 

 as E. Hektwig predicates for the buds and thinks probable for the 

 ovaries. Certainly any such spiral arrangement of the sex organs 

 should be apparent, as well, in the order of the appearance of the 

 testes, when they occur in large numbers, as they frequently do, 

 for the cause assigned for the spiral succession is the depletion of 

 nutrition immediately about the ovary and bud and the consequent 

 necessity of the next bud or ovary occupying a difterent region. I 

 think such an arrangement of the spermaries or ovaries has not 

 been observed. If I am correct in the position taken later in this 

 paper that the sex organs originate from distinct germ cells which, 

 in the mature hydra, are differentiated from the indifterent inter- 

 stitial cells, then such a difference in the order of appearance of 

 the buds and sex organs would be expected as in addition to the 



