4* Notes on the Freshwater Fauna of India* No* X* 



Hydra ovlentnlis during the Rains. 



By N. Anxandale, D.Sc. 



In nij recent account of the Bengal Hydra (Mem. Asiat, Soc. 

 Bengal^ i., No* 16, pp. 339-359; I was able to say very little about 

 that part of the life history which is completed during the rains, 

 z.e., between June and November. During the present year, how- 

 ever, the discovery of a particularly deep and densely shaded corner 

 of the Museum tank to which the polyps migrate during the hot 

 weather, and in which tliey remain until the beginning of winter, 

 has made it possible to study them in their natural surroundings at 

 this season. No individuals which show any sign of sexual 

 niafcui'ity have been found. All have had four tentacles and have 

 been small, attenuated and practically colourless ; but the 

 majority have borne either one or tAvo four-tentacled buds. I had 

 not previously seen a four-tentacled polyp budding. It thus be- 

 comes clear that what may be called the summer phase of //. 

 orientalU has habitually four tentacles and that after undergoing 

 a period of rest in June it produces buds like itself, which are 

 coloirrless and with four tentacles. I have been unable to obtain 

 any evidence that the polyp produces additional tentacles after 

 fiving rise to a bud, and it is probable that the individuals which 

 become densely pigmented at the end of October or in November, 

 grow two additional tentacles and bear buds, are the offspring of 

 the individuals which ai^ise asexually in May or June. 



'1 he life cycle of H. orientalis affords an example of what 

 may perhaps be regarded as an extremely simple form of alterna- 

 tion of generations. The four-tentacled summer phase gives rise 

 asexually to the six- tentficled winter phase, which is potentially 

 sexual. The latter phase, however, gives rise to the former again 

 asexually as a rule, possibly by sexual reproduction occasionally. 

 'J'here are intermediate generations which are intermediate ia 

 structure as well as time, and the whole cycle has evidently been 

 influenced if not produced by degeneration due to an nnfavoui'al)le 

 climate. It seems probable that the genus has reached tropical Asia 

 from more temperate latitudes, in which it exhibits far great ta^ 



vigour in several directions. 



When I wrote the paper alluded to above I had not seen 

 Prof. Br- Hertwig's recent account ^ of his experiments on H, fusca^ 

 Afhich was only published on August 1st, almost exactly at the 

 same date as my paper. Prof. Hertwig proves by direct experi- 

 ment that in the cavse of the species with which hede:»l8, seemingly 

 hermaphrodite individuals may, under certain conditions, become 

 apparently dioecious. He therefore rejects Downing's H, dicpcui 

 as a distinct species, apparently with justice. My H. oriental is 

 certainly bears (or boie in the earlier stages of its erolution) a 



1 " Ueber Knospntig and Geschlechtsentwickelnn^ von Hydra fnsoa," In- 

 Biologisches Centralblatt^ nxvi., yo. 16 (Ancrnst Ist, 1906). 



