Several Indian sponges are only found adhering to stones and rocks. Among these species _Corvospongilla lapidosa_ and our representatives of the subgenus _Stratospongilla_ are noteworthy. Some forms (e. g. _Spongilla carteri_ and _S. crateriformis_) seem, however, to be just as much at home in muddy as in rocky localities, although they avoid the mud itself. There is much indirect evidence that the larvæ of freshwater sponges exercise a power of selection as regards the objects to which they affix themselves on settling down for life. Few Spongillidæ are found in salt or brackish water, but _Spongilla alba_ var. _bengalensis_ has been found in both, and is abundant in the latter; indeed, it has not been found in pure fresh water. _Spongilla travancorica_ has only been found in slightly brackish water, while _S. lacustris_ subsp. _reticulata_ and _Dosilia plumosa_ occur in both fresh and brackish water, although rarely in the latter. The Spongillidæ are essentially a freshwater family, and those forms that are found in any but pure fresh water must be regarded as aberrant or unusually tolerant in their habits, not as primitive marine forms that still linger halfway to the sea. ANIMALS AND PLANTS COMMONLY ASSOCIATED WITH FRESHWATER SPONGES. (a) _Enemies._ Freshwater sponges have few living enemies. Indeed, it is difficult to say exactly what is an enemy of a creature so loosely organized as a sponge. There can be little doubt, in any case, that the neuropteroid larva (_Sisyra indica_) which sucks the cells of several species should be classed in this category, and it is noteworthy that several species of the same genus also occur in Europe and N. America which also attack sponges. Other animals that may be enemies are a midge larva (_Tanypus_ sp.) and certain worms that bore through the parenchyma (p. 93), but I know of no animal that devours sponges bodily, so long as they are uninjured. If their external membrane is destroyed, they are immediately attacked by various little fish and also by snails of the genera _Limnæa_ and _Planorbis_, and prawns of the genus _Palæmon_. Their most active and obvious enemy is a plant, not an animal,--to wit, a filamentous alga that blocks up their canals by its rapid growth (p. 79). (b) _Beneficial Organisms._