igig-] N. AnnandaIvE : Bombay Streams Fauna. 157 



the lax branches of Spongilla lacustris may be observed hanging 

 in the water of placid streams such as the Isis at Oxford, the onl^^ 

 branched form from running water that I can call to mind in the 

 tropics is the South American Uruguaya, in which the skeleton is 

 of coralline hardness. In the creeks of the Gangetic delta 

 Spongilla alba may seem to be a branched form even when the 

 water is moved by sluggish currents. It is not really so, but an 

 encrusting sponge covering the roots or stems of grasses. 



The sponges of Indian streams vary considerably both in 

 external appearance and in internal structure. As a rule they are 

 either of a vivid leaf-green colour or of a dense purplish-brown or 

 black. They may be either soft or extremely hard , they usually 

 spread over considerable areas, but are sometimes confined to 

 pockets in the rock. Their colour, whether black or green, is due 

 to the presence of large numbers of minute organized bodies in 

 their cells. These bodies probably represent in all cases a stage 

 in the life history of a microscopic alga, but whether the green 

 corpuscles are all specifically identical we do not know, and no 

 investigation has been made of the purple corpuscles which cause 

 the darker colour. Black or brown sponges occur together with 

 green ones and though their colour has no generic significance, it 

 appears to be, in spite of its quasi-parasitic origin, of specific 

 importance. 



All the green sponges from rocky streams with which I am 

 acquainted have apeculiir type of circulatory system that is often 

 to be found in thin encrusting sponges, not only among the Spongil- 

 lidae but also in several marine Tetraxonid families. In this type 

 the pores, which are usually of relatively large size, are arranged 

 in more or less circular groups immediately over the mouths of 

 relatively wide inhalent canals, which run vertically downwards 

 to near the base of the sponge, giving off lateral channels which 

 convey the incoming water to the ciliated chambers. The 

 exhausted water returns through other channels of similar calibre 

 to the surface of the parenchyma, where it enters relatively wide 

 horizontal canals that ramify immediately below the dermal 

 membrane, which forms their roof. Each system has an osculum 

 situated near the centre of these ramifying channels. It is never 

 of large size and is always protected by a conical dermal collar, 

 which is highly contractile and disappears in preserved specimens. 

 This type of circulatory system is found among marine sponges 

 that encrust rocks in shallow water and is by no means peculiar 

 to green species; among the Spongillidae it is also found in almost 

 colourless lacustrine species that grow near the edge of lakes on 

 the lower surface of stones. Its development has no taxonomic 

 significance but appears to be correlated with growth in the form 

 of a thin layer on smooth surfaces in situations in which there is 

 considerable movement in the water and danger from the accumu- 

 lation of silt. 



I collected specimens of the following species in the Satara 

 and Poona districts and in Chota Nagpur : — 



