162 BRITISH SPONGES: 



seminal capsules. This state of it has been by many reckoned 

 a distinct species, but the inconstancy and pliancy of the Spon- 

 gilla is so great, that I readily assent to the opinion of Gervais, 

 Blainville and others, who believe that even the most dissimi- 

 lar of its forms are dependant on the varying influence of ex- 

 ternal circumstances. I have not been able to detect any es- 

 sential difference in texture, or in the form of the spicula. 



Dr R. D. Thompson, on an analysis of this species, found 

 it to consist of, 



Organic matter, 



26. 



Silica, 



50.66 



Carbonate of lime, 



13.0 



Pfiosphate of lime, 



10.1 



Alumina, 



. a trace. 



99.86 



According to Gmelin the powder of Sp. fluviatilis is employ- 

 ed as a veraiifuge in Russia. 



2. Sp. lacustris, " hard, brittle, and coarsely Jibrous ; 

 spicula linear and doubly pointed.''^ 



Spongia lacustris, " Don's Animals of Forfarshire, 36." 

 Halichondria lacustris, Flem. Brit. Anim. 324. 



Hab. " In lakes in Angus and Fife," Fleming. 



" Massive, rising into short rounded branches : the fibres are 

 coarser, and the substance denser than the preceding ; the spi- 

 cula, too, though similar in form, are thicker, and about one- 

 fourth shorter." Fleming. — This difference in the spicula ap- 

 pears to prove the distinctness of this species, with which I am 

 not acquainted. 



I may here remark that some of the descriptions given of 

 fresh-water sponges seem to have been derived from states of 

 Alcyonella stagnorum. It is from a mistake of this kind that 



