THE REACTION OF HYDRA TO INANITION. l8l 



material must be handed directly, in the form of food, to the 

 endoderm of the tentacle-bases. 



SUMMARY. 



Hydra, as a diploblastic animal, can have no circulatory 

 medium. Perhaps for a similar reason it can have no storage 

 tissue such as fat. Green Hydras seem able to fall back upon the 

 surplus foods of its zoochlorellse, for, contrary to some observers, 

 it has been our experience that Hydra viridis is much less influ- 

 enced by inanition than other species. 



In all species, if the inanition be prolonged and the individuals 

 be kept free from parasites and concentrated toxins, each 

 specimen not getting food, will begin to feed upon its tentacles. 

 First the ends of the tentacles are bitten off. If now food is yet 

 with-held from the Hydra, it will feed upon its tentacles until but 

 the merest stumps are left. 



The ingested tentacles will be digested. Even the nematocysts 

 (both types) will be taken into food-vacuoles within the epithelio- 

 muscular cells and be completely digested and absorbed. 



After the Hydra has thus fed upon and appropriated its 

 tentacles except for mere stumps that stand about the peri- 

 stome the bases of the amputated tentacles will regenerate and 

 the Hydra, now reduced in size, will possess a new group of 

 tentacles. 



In feeding upon the tentacles that have been ingested, the 

 endoderm of the stumps of tentacles appropriate relatively more 

 of the ingested tentacle-material than is appropriated by the 

 endoderm of the body proper. This appears to be correlated 

 with the fact that regeneration is to take place in the tentacular 

 stumps. 



LITERATURE. 

 Annandale, N. 



'07 Seasonal Variations in Hydra Orientalis. Journ. and Proc. Asiatic Soc. 



Bengal, N. S., III. 

 Berninger, von Julius. 



'10 Uber Eimvirkung des Hungers auf Hydra. Zool. Anz., Bd. 36. 

 Entz, G. 



'12 Uber eine neue Amobe auf Susswasser Polpen (Hydra Oligactis Poll). 



Arch. Protistenk., Bd. 27. 

 Glaser, O. G. and C. M. Sparrow. 



'09 The Physiology of Nematocysts. J. Exp. Zool., Vol. 6. 

 Huxley, J. S. and G. R. De Beer. 



