The two species that flourish all the year round do not, properly speaking, belong to one category, for whereas _Hislopia lacustris_ produces no form of resting reproductive body but bears eggs and spermatozoa at all seasons, _Spongilla proliferens_ is a short-lived organism that undergoes a biological crisis every few weeks; that is to say, it begins to develop gemmules as soon as it is fully formed, and apparently dies down as soon as the gemmules have attained maturity. The gemmules apparently lie dormant for some little time, but incessant reproduction is carried on by means of external buds, a very rare method of reproduction among the freshwater sponges. The facts just stated prove that considerable specific idiosyncrasy exists as regards the biology of the sponges, hydroids, and polyzoa of stagnant water in Bengal; but an even more striking instance of this phenomenon is afforded by the sponges _Spongilla bombayensis_ and _Corvospongilla lapidosa_ in Bombay. These two sponges resemble one another considerably as regards their mode of growth, and are found together on the lower surface of stones. In the month of November, however, _C. lapidosa_ is in full vegetative vigour, while _C. bombayensis_, in absolutely identical conditions, is already reduced to a mass of gemmules, having flourished during the "rains." It is thus clear that the effect of environment is not identical in different species. This is more evident as regards the groups of animals under consideration in India (and therefore probably in other tropical countries) than it is in Europe. The subject is one well worthy of study elsewhere than in India, for it is significant that specimens of _S. bombayensis_ taken in November in S. Africa were in a state of activity, thus contrasting strongly with specimens taken at the same time of year (though not at the same season from a climatic point of view) in the Bombay Presidency. GEOGRAPHICAL DISTRIBUTION OF THE INDIAN SPECIES.