In Calcutta two broods can be distinguished, a cold-weather brood, which is larger, stouter, and more deeply coloured, produces buds more freely, has larger nematocysts, and as a rule possesses 6 tentacles; and a hot-weather brood, which is smaller, more slender and paler, produces buds very sparingly, has smaller nematocysts, and as a rule possesses only 4 or 5 tentacles. Only the cold-weather form is known to become sexually mature. There is evidence, however, that in those parts of India which enjoy a more uniform tropical climate than Lower Bengal, polyps found at all times of year resemble those found in the hot weather in Calcutta, and sometimes produce spermatozoa or eggs. I have recently had an opportunity of comparing specimens of the Calcutta hot-weather form with well-preserved examples of _H. vulgaris_, Pallas (=_H. grisea_, Linn.), from England. They differ from these polyps in very much the same way as, but to a greater degree than they do from the winter phase of their own race, and I have therefore no doubt that _H. orientalis_ is merely a tropical phase of Pallas's species. My description is based on Indian specimens, which seem to differ, so far as anatomy is concerned, from European ones in the following points:-- (1) The sexes are invariably distinct; (2) the nematocysts are invariably smaller. I have seen in Burma an abnormal individual with no tentacles. Its buds, however, possessed these organs. TYPE. None of the older types of _Hydra_ are now in existence. That of _H. orientalis_ is, however, in the collection of the Indian Museum. GEOGRAPHICAL DISTRIBUTION.--_H. vulgaris_ is common in Europe and N. America and is probably found all over tropical Asia. The following are Indian and Ceylon localities:--BENGAL, Calcutta and neighbourhood (_Annandale_, _Lloyd_); Adra, Manbhum district (_Paiva_), Rampur Bhulia on the R. Ganges (_Annandale_); Chakradharpur, Chota Nagpur (_Annandale_); Pusa, Bihar (_Annandale_); Puri, Orissa (_Annandale_): MADRAS, sea-beach near Madras town (_Henderson_): BOMBAY, island of Bombay (_Powell_): BURMA, Mandalay, Upper Burma, and Moulmein, N. Tenasserim (_Annandale_): CEYLON, Colombo and Peradeniya (_Willey_, _Green_). Dr. A. D. Imms tells me that he has obtained specimens that probably belong to this species in the Jumna at Allahabad. BIOLOGY.--In India _H. vulgaris_ is usually found, so far as my experience goes, in stagnant water. In Calcutta it is most abundant in ponds containing plenty of aquatic vegetation, and seems to be especially partial to the plant _Limnanthemum_, which has floating leaves attached to thin stalks that spring up from the bottom, and to _Lemna_ (duckweed). Dr. Henderson, however, found specimens in a pool of rain-water on the sea-shore near Madras.