THE REACTION OF HYDRA TO INANITION. 



W. A. KEPXER AND P. N. JESTER, 

 UNIVERSITY OF VIRGINIA. 



During the past fifteen years the senior author has observed 

 that Hydra, kept in laboratory aquaria to which food has not been 

 added, decreased greatly in size. In this general or casual 

 observation, it was further noticed that green Hydras survived 

 under these adverse conditions for much longer periods than did 

 Hydras of other species. This has been a general experience in 

 this laboratory, though it stands in sharp contrast with Wagner's 

 ('04) statement that "Green Hydras stand starving very poorly, 

 usually perishing in two or three days" (p. 612). In later years 

 it was observed further that the poorly fed Hydras would lose 

 parts of their tentacles. Sometimes the full complement of 

 tentacles has disappeared. During the last three years, we have 

 been seeking to learn the conditions under which Hydras lose 

 their tentacles. ' 



The literature presents the following causes by which Hydras 

 lose their tentacles. N. Annondale ('07), in studying Hydra 

 orientalis, found a seasonal variation from four to six tentacles. 

 During the hot season this Hydra has but four tentacles, while 

 during the cold part of the year it has six tentacles. G. Entz 

 ('12) observed that an infection with Amceba hydroxena may lead 

 to a complete loss of tentacles. E. Reukauf ('12) observed that 

 the ciliate Prodon teres caused Hydra to lose its tentacles. Again, 

 the presence of another ciliate, Kerona pediculus, according 

 to P. Schultze ('13), leads to hypertrophy of the tentacles. E. 

 Schultz ('06) observed that hunger set up a process of dedifferenti- 

 ation within the tentacles of Hydra; just as Huxley and De Beer 

 ('23) found that hunger and toxins caused dedifferentiation and 

 resorption of the tentacles of Obelia and Campanulana. Huxley 

 and De Beer observed that this process of dedifferentiation and 

 resorption might involve, not only the tentacles, but also part of 

 the zooid. Finally Berninger ('10) observed that, in response to 

 inanition, Hydra lost its tentacles; but he did not see the man- 

 ner in which they were lost. 



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