BRITISH SPONGIAD^. 53 



extent. The ternate terminations are embedded in the 

 inner surface of the crustular dermis, and the shaft passes 

 into the body of the sponge beneath, at right angles to the 

 surface, thus securely bracing the two parts of the sponge 

 together, and forming areas for the valvular proximal 

 terminations of the intermarginal cavities. The oscula 

 frequently assume a linear arrangement on the elevated 

 ridges of the surface. In the live state they are even with 

 the surface of the sponge, and are furnished with a mem- 

 branous veil, which apparently has the power of contrac- 

 tion, so as to entirely close the osculiim at the will of the 

 animal. In the dried condition they are frequently sur- 

 rounded by a slightly elevated ring, arising from the 

 contraction of the membranous veil in drying. They are 

 very numerous, but rarely exceed the eighth of an inch in 

 diameter. 



In the living condition, the pores are not visible to the 

 unassisted eye, but in the dried state they are very distinctly 

 to be seen. They are very numerous, and occupy every 

 part of the surface, excepting in the immediate vicinity of 

 the oscula, near which they appear to be smaller than they 

 are in the more distant portions of the space intervening 

 between the groups of those organs. The normal form of 

 the skeleton spicula is regularly cylindrical, with hemi- 

 spherical termination of the same diameter as the shaft, 

 but sometimes one or both of the terminations will be in- 

 creased in diameter, so as to become sub-clavate, and at 

 others, if it were not for the sub-hemispherical terminations 

 of the lesser end, the form would be completely acuate ; or 

 we find the terminations sub-hemispherical and the shaft 

 fusiform, to a considerable extent. 



The arrangement of the interstitial membranes in the 

 body of the sponge is strikingly similar to the mode of 

 disposition of the membranous structure in the human lung 

 when in a state of distension, and like it, they form the 

 walls of continuous, irregular, and very much contorted 

 cavities. When free of sarcode by maceration, they are 

 thin, transparent, and destitute of spicula. In the living 

 state the sarcode is in great profusion, and it is furnished 



