In an Indian pond or lake a similar crisis takes place in the case of most species, but it does not take place at the same time of year in the case of all species. Unfortunately the phenomena of periodic physiological change have been little studied in the freshwater fauna of most parts of the country, and as yet we know very little indeed of the biology of the Himalayan lakes and tarns, the conditions in which resemble those to be found in similar masses of water in Europe much more closely than they do those that occur in ponds and lakes in a tropical plain. In Bengal, however, I have been able to devote considerable attention to the subject, and can state definitely that some species flourish chiefly in winter and enter the quiescent stage at the beginning of the hot weather (that is to say about March), while others reach their maximum development during the "rains" (July to September) and as a rule die down during winter, which is the driest as well as the coolest time of year. The following is a list of the forms that in Bengal are definitely known to produce hard-shelled eggs, gemmules, resting-buds, or statoblasts only or most profusely at the approach of the hot weather and to flourish during winter:-- _Spongilla carteri._ _Sponging alba._ _Spongilla alba_ var. _bengalensis_. _Spongilla crassissima._ _Hydra vulgaris._ _Victorella bengalensis._ _Plumatella fruticosa._ _Plumatella emarginata._ _Plumatella javanica._ The following forms flourish mainly during the "rains":-- _Spongilla lacustris_ subsp. _reticulata_. _Trochospongilla latouchiana._ _Trochospongilla phillottiana._ _Stolella indica._ The following flourish throughout the year:-- _Spongilla proliferens._ _Hislopia lacustris._ It is particularly interesting to note that three of the species that flourish in the mild winter of Bengal, namely _Hydra vulgaris_, _Plumatella emarginata_, and _P. fruticosa_, are identical with species that in Europe perish in winter. There is evidence, moreover, that the statoblasts of the genus to which two of them belong burst more readily, and thus give rise to new colonies, after being subjected to a considerable amount of cold. In Bengal they only burst after being subjected to the heat of the hot weather. Does extreme heat have a similar effect on aquatic organisms as extreme cold? There is some evidence that it has. The species that flourish in India during the rains are all forms which habitually live near the surface or the edge of ponds or puddles, and are therefore liable to undergo desiccation as soon as the rains cease and the cold weather supervenes.