174 W - A ' KEENER AND P. N. JESTER. 



We have found that Hydra is very susceptible to the impulses 

 arising from scarcity of food. Hydras, at the time they are 

 taken from the pond, present sometimes one or more fragmentary 

 tentacles. That these do not represent mere accidental losses is 

 suggested by the fact that in a flourishing population of Hydras 

 one does not readily meet with such imperfect specimens, 

 whereas when the population of a pond is on the decline specimens 

 with incomplete tentacles are quite frequently encountered. 



That Hydras react rather readily to hunger is further indicated 

 by the observations of Wilson ('91). He records that "After the 

 exhaustion of the food-animals which takes place rapidly when 

 the Hydras become very numerous the Hydras are compelled 

 to live wholly upon mud" or sediment at the bottom. In this 

 sediment they find fragments of plant tissue and numerous 

 minute Infusoria. The polyps, "after descending, usually gorge 

 themselves with the sediment at the bottom." Welch and 

 Loomis ('24) verified this observation. They found, however, 

 "that the Hydras did not always thrive indefinitely on the 

 sediment material dredged from the deepest parts of the lake," 

 p. 227. 



Realizing, then, the susceptibility of Hydra to hunger, we set 

 to work to see if inanition was a factor leading to the loss of 

 tentacles. This effort was made through the observation of 

 living isolated individuals and the histological study of isolated 

 individuals and controls. 



Hydra has been observed taking into its body a tentacle's end 

 as it clung to the food. This has been seen frequently. For 

 example Mr. J. W. Nuttycombe saw a Hydra swallow the ends 

 of two tentacles that had been involved in the capture of a 

 Cyclops. After considerable struggle on the part of both the 

 tentacles and the body-proper, these tentacles were thrown from 

 the crelenteron. So far as could be determined these tentacles 

 had not been injured. In such examples, an effort to free the 

 tentacle from the coelenteric cavity is always apparent. 



In contrast to this, Mr. M. C. Yoder and the senior author 

 observed an isolated Hydra, that had been deprived of food, hold 

 a tentacle within the ccelenteric cavity for twenty minutes. 

 Throughout this period the tentacle remained quiet. There was 



