THE REACTION OF HYDRA TO INANITION. 



to the water in which the unfed specimens were kept. However, 

 a second series of observations was made. In this series, five 

 specimens were isolated and carried through unfed while five 

 isolated specimens were fed to serve as controls. Each day the 

 water in all watch-glasses containing Hydras was areated by- 

 blowing air through it and every twenty-four hours or every 

 forty-eight hours the old water was drawn off and fresh spring 

 water added. In these instances, we got just as conspicuous 

 contrast between the unfed series and the fed series as has been 

 described for the series running from March 14 to April 13. The 

 most pronounced example, obtained in this manner of Hydra's 

 reaction to inanition, was obtained from specimen 4 of a series 

 begun October 6, 1925, and ending October 30. A camera lucida 

 drawing w r as made of this specimen as it hung from the surface of 

 the w r ater in the watch-glass, October 6 (Fig. 6). Three days 

 later the camera lucida drawing shows that there had been a 

 marked reduction in the size of the specimen (Fig. 6). On 

 October 1 1 , the specimen presented only mere stumps of tentacles 

 (Fig. 6). Camera lucida outlines made daily showed that those 

 tentacle stumps gradually grew until by October 22 the camera 

 lucida outline reveals that the now smaller Hydra had regener- 

 ated seven tapering tentacles (Fig. 6). The next day, however, 

 one of these tentacles had disappeared (Fig. 6). A second 

 tentacle was missing October 24 (Fig. 6). Two days later the 

 camera lucida drawing indicates that the specimen had lost the 

 greater part of each of its tentacles (Fig. 6). In this condition 

 the specimen remained as a listless individual for three days and 

 then died. 



The above specimens were examined daily for the presence 

 of parasites such as Amcsba and other protozoa and were thus 

 determined to have been free of such infection. The abruptness, 

 however, with which a part of a tentacle or a whole complement 

 of tentacles would be lost did not suggest that these tentacles 

 disappeared through attack by parasites or by degeneration and 

 resorption. It suggests rather that the specimens had been 

 feeding upon their tentacles. 



The histological evidence supports the idea that dedifferenti- 

 ation, degeneration and parasites were not involved. 



