The Common Hydra of Bengal : its Systematic Position and Life History. 



By N. Annandale, B.A. (Oxon), D.Sc. (Edin.), C.M.Z.S., Officiating 



Superintendent of the Indian Museum and Professor of Zoology in the 



Bengal Medical College. 



[Read June 6th, 1906.] 

 Contents. 



I. Systematic Position and Distribution — Page. 



The Structure of Hydra orientalis 339 



The species of Hydra 341 



Distribution of the genus in Asia 342 



II. Life History — 



Reproduction and duration of life 343 



Favourable and unfavourable conditions 352 



Feeding 354 



Movements 355 



Colour 358 



Summary 359 



In 1905 I called attention to the existence of a species of Hydra in Bengal, which I 

 named provisonally Hydra orientalist and more recently 2 I have published additional 

 specific characters of this species, but only in a condensed form. As I propose in the 

 present communication to deal with the peculiarities in the structure and life history 

 of the Bengal form, it has been unnecessary to describe in detail structures and 

 phenomena well known and undisputed in other species of the genus. 



I. 



Structure. 



Hydra orientalis is an ordinary member of its genus as regards structure. It has a 

 slender cylindrical body, which is not less than thirty times as long as broad when normal- 

 ly extended and has a slightly smaller diameter at the base than towards the mouth. 

 (When food has been swallowed recently these characters are not apparent.) In the adult 

 the number of tentacles is either five or (more commonly) six ; while the young polyp 

 has five, four, or only three. The tentacles are capable of great extension, sometimes 

 being six times as long as the body, and more commonly three times as long ; they are 

 not dilated at the tip. H. orientalis is dioecious. The male produces some four to 

 twenty-four spermaries. Two kinds of eggs are borne by the female, often on the same 

 individual and almost simultaneously. One kind, which is probably pathological, has 

 a thin, smooth surface with a small projection at the pole furthest from the point of 

 attachment to the parent, while the other has a thick outer shell set with slender spine s 



1 Journ. Asiat. Soc Bengal, 1905, p. 72. - Ibid., 1906, p, 109. 



Mem. A.S.B. 25-7-06. 



