296 Elliot E. Downing, 



Material. 



The bulk of the work has been done on Hydra dioecia with 

 abundant U. fusca for comparison; I have also had the ovaries of 

 H. (jrisea and H. viridis under frequent observation, both in living- 

 and preserved material. The animals have been collected at several 

 localities. At Chicago, 111., I have obtained all four species, all 

 but H. (jrisea with eggs; at Beloit, Wise, I have collected U. fusca 

 and H. viridis, both sexually' mature; at Marquette, Mich., all four 

 species with ovaries and spermaries. I have collected, in the park 

 ponds of New York City, H. viridis, H. fusca and H. grisea and, 

 through the kindness of Mr. D. I). Whitney, have received H. dioecia 

 from ponds on the Palisades, opposite the city, in New Jersey. 



Species. 



R. Heetwig has criticised me (20) for separating Hydra dioecia 

 from H. fusca. He thinks such separation is premature, at least, 

 and prefers to regard the form I have named H. dioecia merely a 

 dioecious condition of H, fusca. He says, "Er [Downing] nennt die 

 hermaphrodite Form H. fusca, die getrennt geschlechtliche H. dioecia. 

 Ich billige das Verfahren Downing's nicht. Wir wissen noch zu 

 wenig-, ob Hermaphroditismus und Gonochorismus immanente Charactere 

 der verschiedenen Hydra-Arten sind oder nicht die Konsequenzen 

 ihrer Existenzbedingungen im weitesten Sinne des Wortes, so daß 

 je nach der Einwirkungsweise derselbe hermaphrodite, rein männ- 

 liche oder rein weibliche Individuen entstehen würden. ... So lauge 

 wir über diese Dinge noch nicht genügend orientiert sind, ist es nicht 

 ratsam, dem Hermaphroditismus oder Gonochorismus Bedeutung für 

 die systematische Unterscheidung verschiedener Hydraavten bei- 

 zumessen."' How m-ànj specific names would be given were we to 

 wait until we are thoroughly oriented on the physiological factors 

 which condition specific differences! 



Permit me again to state that it is not alone on the basis of 

 a constant distinction of the sexes that the new specific name was 

 given. H. dioecia differs from H. fusca in other respects: its size 

 is, on the average, notably greater; the length of its tentacles, in 

 proportion to body length, is greater; its embryo shell is spherical 

 while that of H. fusca is strongly flattened after attachment. I 

 suggest, now, this added point of difference. So far as my own ob- 

 servations go, H. dioecia is the only hydra which habitually bears 



