I9 r 5-] Fauna of the Chilka Lake ; Sponges. 20 



The species may be described as essentially an encrusting sponge, but short 

 branches, as a rule distinctly compressed rather than cylindrical, often arise from 

 the surface. Sometimes they are so thin as to be almost filamentous, often they are 

 short and stout and of irregular, triangular or trilobed cross-section (pi. v, fig. i). 

 In most cases these branches (pi. iii) are mere crusts enclosing fine filaments of algae 

 or the stems of water plants, but sometimes it is not possible to detect in them any 

 extraneous core. 



In the phase that occurs on rocks in the Chilka Lake the larger waterways 

 have a distinctly radial arrangement and the main exhalent channels converge, near 

 and on the surface of the parenchyma, to a central primitive osculum. The external 

 surface has a reticulate appearance owing to the arrangement of the skeleton and the 

 meshes are often distinctly longer in the direction of the exhalent channels than in any 

 other. The inhalent channels are vertical in direction and are conspicuous in the 

 dried sponge as circular pits extending downwards from the surface. The dermal 

 pores are scattered and very minute. They have the unicellular structure character- 

 istic of the family. 



5. alba has been found in fresh water at several widely separated localities in 

 India: the island of Bombay, the Western Ghats, Calcutta, and Hyderabad: also 

 near Cairo in Lower Egypt ; nowhere does it appear to be of common occurrence 

 in ordinary ponds and lakes. It is, however, extremely abundant in brackish 

 water in the Gangetic delta and has been found in the same medium on the 

 west coast of India in the backwaters of Cochin. In the Chilka Lake its distribution 

 is somewhat remarkable It occurs on all the rocks of the northern region, often 

 growing luxuriantly and covering considerable areas, and is found among loose algae 

 in the outer channel. In sheltered inlets among the rocks its gemmules often form a 

 scum on the surface. South of Kalidai Id it is not present in the lake, although 

 many rocks apparently suited for its growth are situated round Rambha Bay. It 

 does grow, however, in a small pool of practically fresh water on Barkuda Id. Even 

 on Kalidai, on the north side of which it is common, we did not find it on the 

 south side. A very careful search at low water on Maludaikuda Id. failed to reveal 

 a single specimen, and no gemmules could be detected on the surface of the water. 

 The sponge evidently flourishes best at depths of from 2 to 10 feet. We found it 

 growing actively and producing larvae in water of a sp. gr. of 1-0065, but it cannot 

 exist in water that never becomes fresh or practically fresh ; specimens taken in salt 

 water in the outer channel were all dead. 



The larvae are of the true Spongillid type and resemble those of S.lacustris in 

 their ovoid shape. 



The colour of S. alba varies greatly but depends on external circumstances. As 

 its name indicates, the sponge is, when growing in clean water, of a glistening white 

 very characteristic in its purity, but if the water it inhabits is muddy, as is usually 

 the case, it assumes the hue of the surrounding soil. In the pond on Barkuda Id., 

 where the earth and rocks contain much iron, it is reddish; in the lake and in the 

 creeks and canals of the Gangetic delta it is grey, but this tint is usually concealed 



