i9*5-] 



Fauna of the Chilka Lake : Sponges. 



27 



transverse ones or even by single spicules: at places there is also an irregular 

 network of single spicules or very fine fibres. At all points at which spicules of the 

 skeleton meet one another at an angle there is a more profuse secretion of horny sub- 

 tance, which there forms a kind of veil 1 often produced for some little distance along 

 the surface of individual spicules. 



In the typical form of 5. alba (i.e. the form represented by the type specimen, 

 which is from fresh water on the island of Bombay) the structure of the skeleton 

 is essentially the same, but the radiating fibres branch and anastomose more freely 

 and the transverse ones are more numerous , so that a closer and harder network is 

 formed. Moreover, the subsidiary skeleton of single spicules to which I have alluded 

 already is characteristic, in its full development, of the harder phases of this species, 

 although but slight traces of it can be detected in the more fragile forms thereof. 



%^0^-^ße^a^^^ : ' " ^ 



Fig. 1. — Spongilla alba, Carter. 

 Vertical section of a moderately hard sponge from Pigeon Id. in the Chilka Lake, x 30. 



If a long series of specimens from different localities be examined it will be found that 

 some of them agree in skeletal structure almost precisely with the typical 5. lacustris. 

 In the Chilka Lake and its immediate vicinity we obtained specimens not only pro- 

 viding a complete transition, but even going further in some cases than the typical 

 5. lacustris in the direction of simplicity of skeleton, and, in other cases, than the 

 typical 5. alba in that of complexity. In simple forms the secretion of horny 

 matter is much reduced and it does not produce veil-like films at the nodes of the 

 skeleton (see pi. iv, figs. 1,2, and pi. v, fig. 1). 



Neither the spicules nor the gemmules afford any constant differential character. 

 The macroscleres are simple, sharply pointed, smooth amphioxi, very variable in size 



1 Apparently this veil is never deposited in distinct concentric layers as in Lubomirskia, cf. Annan- 

 dale, Rec. Ind. Mus. X, p. 144, pi. ix, fig. 1« (1914). 



