of the Freshwater Sponges in the Tanks of Bombay. 305 



abounds in spicula, as in No. 2, wliere they are mostly spini- 

 ferous, and in No. 4, where they are of the curious stellated form 

 described. There are also, in addition, little sac-like bodies which 

 are ever changing their form and vibrating particles, both of 

 which will be hereafter mentioned. If a portion of the mem- 

 brane be carefully held before the blowpipe under a red heat, 

 the animal matter may be driven off, while the forms of the 

 bodies mentioned appear to remain unaltered ; sometimes even a 

 siliceous skeleton of the membrane itself may remain, so tho- 

 roughly does silex pervade every portion of its structure. But 

 there is a transparent reticulated network (probably filamentous) 

 which can only be seen when the membrane is fresh. 



Spicula. — The smooth spicula and the spicula terminated by 

 toothed discs are hollow. In the smooth spiculum the form of 

 its cavity may be seen by charring the animal matter which lines 

 its interior. It will be found to be wide in the body of the spi- 

 culum, and to terminate abruptly at each end in a linear con- 

 tinuation. I have not been able to see it in the spiniferous spi- 

 cula, on account of the number of little spines which encrust 

 them. 



The small spicula in each species are principally derived from 

 the crusts of its seed-like bodies. In all the species the spicula 

 are siliceous, and the largest are so much alike that they are of 

 no use as a specific distinction. 



Seed-like bodies. — The seed-like bodies are spherical or ovoid, 

 according to the species. They all present an infundibular de- 

 pression communicating with their interior ; when young they 

 are transparent and filled with minute granules like the vibrating 

 bodies to be hereafter mentioned ; as they get older, a crust of 

 siliceous spicula, arranged perpendicularly to their surface, is se- 

 creted from their external membrane ; it is from this crust that 

 the small spicula in the dificrent species are principally derived. 

 In Nos. 1 and 2 they are straight, or slightly curved, and spini- 

 ferous. In Nos. 3 and 4 they are straight, sometimes spini- 

 ferous, and terminated at each end by a toothed disc ; the discs 

 of their free extremities surmount little papillary projections on 

 the surface of the seed-like body, and they present a hole in their 

 centre, which communicates with the cavity of the spiculum on 

 which they are supported ; their fixed ends are applied by a simi- 

 lar disc to the silicifying or external membrane of the seed-like 

 body. The latter is coriaceous, and presents a hexagonally tes- 

 sellated appearance, on which rest the fixed discs of the spicular 

 crust. I could not perceive any holes in the centres of these 

 hexagonal divisions. 



Before the seed-like body arrives at its state of maturity, it is 

 filled with minute granules suspended in a viscid transparent 



