30 



Memoirs of the Indian Museum. 



[Voi,. V, 



by a dull green flush sometimes so strong as to predominate. In these cases the 

 colour is due to nothing inherent in the sponge but either to minute particles of silt in 

 its parenchyma cells or to the growth in its substance of green filamentous algae, 

 which belong to several quite distinct groups. In the Chilka Lake a chain-forming 

 diatom is often responsible for the green tint. 



In its power of engulfing particles of silt without apparent detriment to itself 

 this sponge shows itself peculiarly adapted for existence in muddy water in which 

 the solid particles are extremely small, as is the case both in the lake and in most 

 other places at which it has been found. The minuteness of its dermal pores l 

 doubtless serves a similar purpose, or at any rate saves it from being overwhelmed 



ß 



VJ 



ft 



Fig. 2. — Spongilla alba, Carter. 

 Spicules of a normal specimen from the Chilka Lake, x 255. 



by the deposition of silt. The green algae that grow in it are parasitic, or at any rate 

 incidentally destructive. 2 



Where rocks occur 5. alba is literally attracted to them, for as the gemmules are 

 set free from the sponge by the gradual disintegration of its skeleton , they gravitate 

 towards the rocks on the same principle that floating bodies of all kinds are 

 attracted one to another or to fixed objects. Their liberation takes place, owing to 

 the decay of the sponge and the disintegration of the skeleton on the death of its 

 cells, mainly between February and June, but may occur at any time of the year, 



1 These pores have been actually observed, so far as S. lacustris is concerned, only in the var, 

 proliferens. See J own. As. Soc. Bengal (n. s.) IX, p. 69, pi. v, fig. 1 (1913), 



See Faun. Brit. Ind., Freshw* Sponges, etc., p. 49 (1911). 



