BRITISH SPONGIADiE. 19 



sponge, and of the vivid action of the cilia within their 

 margins, is one of the most interesting sights afforded by 

 this tribe of animals. The whole of the phenomena at- 

 tendant on this operation will be found described at length 

 in my paper " On the Ciliary Action of the Spongiaclse," 

 published in the ' Transactions of the Microscopical Society 

 of London,' vol. hi, p. 137. It is exceedingly difficult to 

 get a good view of the pores in this species, they are so 

 completely hidden by groups of flecto-clavate spicula, the 

 distal ends of which curve over the areas in which they are 

 situated, each area being immediately over the distal end 

 of the interstitial cells to which they are appropriated ; they 

 are seen best in. half of a young dried specimen, by trans- 

 mitted light and a linear power of about 250. 



The normal form of skeleton spicula is equiangular tri- 

 radiate, but subject to modification in accordance with the 

 ^necessities of the parts of the structure in which they are 

 situated ; thus, in those which reach the inner surface of 

 the sponge at the united bases of the radii they radiate in 

 an equiangular direction ; the one which passes inward 

 down the sides of the interstitial cells continues straight, 

 but is very much elongated, to give it a firmer hold of the 

 surrounding tissues, while the other two radii, on arriving at 

 the surface, are exflected near the middle of the rays to such 

 an amount as will bury them level with the general plane of 

 the inner surface of the sponge, so that at the basal portions 

 of the radii the spiculum is equiangular, while at the 

 apical portions of two of them they are rectangular, but 

 this mixed form, it must be recollected, is not probably a 

 normal one, but simply a modification of the equiangular 

 triradiate spiculum. 



2. Grantia ciliata, Fleming. 



G. ciliata, Johnston. 



rULVERULENTA, Johnston. 



Sponge. Elongately oval, rarely globular, slightly pedi- 

 celled ; surface papillated, hispid. Cloaca central, 



