I do not know exactly why light and shade must be mixed in a habitat favourable for the growth of sponges, for most species prefer shade, if it be not too dense; but it is certainly the case that, with a few exceptions, Indian Spongillidæ flourish best in water shaded at the edges by trees and exposed to sunlight elsewhere. One of the exceptions to this rule is the Indian race of _Spongilla lucustris_, which is found in small pools of water in sand-dunes without a particle of shade. Several species are only found on the lower surface of stones and roots in circumstances which do not suggest that their position merely protects them from mud, which, as Mr. Potts points out, is their "great enemy." A notable instance is _Trochospongilla pennsylvanica_, which is found hiding away from light in America and Europe as well as in India. It is curious that it should be easy to exterminate the sponges in a pond by cleaning it out, for one would have thought that sufficient gemmules would have remained at the edge, or would have been brought rapidly from elsewhere, to restock the water. Mr. Green has, however, noted that _Spongilla carteri_ has disappeared for some years from a small lake at Peradeniya in which it was formerly abundant, owing to the lake having been cleaned out, and I have made similar observations on several occasions in Calcutta. The question of the objects to which sponges attach themselves is one intimately connected with that of the injury done them by mud. The delta of the Ganges is one of the muddiest districts on earth. There are no stones or rocks in the rivers and ponds, but mud everywhere. If a sponge settles in the mud its canals are rapidly choked, its vital processes cease, and it dies. In this part of India, therefore, most sponges are found fixed either to floating objects such as logs of wood, to vertical objects such as the stems of bulrushes and other aquatic plants, or to the tips of branches that overhang the water and become submerged during the "rains." In Calcutta man has unwittingly come to the assistance of the sponges, not only by digging tanks but also by building "bathing-ghats" of brick at the edge, and constructing, with æsthetic intentions if not results, masses of artificial concrete rocks in or surrounding the water. There are at least two sponges (the typical form of _Spongilla alba_ and _Ephydatia meyeni_) which in Calcutta are only found attached to such objects. The form of _S. alba_, however, that is found in ponds of brackish water in the Gangetic delta has not derived this artificial assistance from man, except in the few places where brick bridges have been built, and attaches itself to the stem and roots of a kind of grass that grows at the edge of brackish water. This sponge seems to have become immune even to mud, the particles of which are swallowed by its cells and finally got rid of without blocking up the canals.