22 A MONOGRAPH OF THE 



was not merely a clean film that might possibly have been 

 formed by a small bubble of sarcode shed from the animal 

 during or after death, but, like the other membranes of the 

 sponge, there were numerous spicula imbedded in its 

 surface, and in this and in other respects of appearance and 

 position the membranes in both cases were alike. It 

 appears, therefore, probable that, besides the closing of the 

 mouth of the cloaca by the approximation of the distal ter- 

 mination of the ciliary spicula, it has also the power of com- 

 pletely closing it by the extension of a veiling membrane, 

 like that of an osculum. 



Since the period of my researches into the ciliary action 

 in Grantia cov/pressa I have not had G. ciliata in a living- 

 condition, and the precise characters of the oscula are not 

 so readily to be seen in the dried specimens in the latter 

 species as in the former one ; but there is a great similarity 

 between them, and I have little doubt but that if a speci- 

 men of G. ciliata were to be divided longitudinally and 

 placed in a cell with fresh cold salt water, and viewed as a 

 transparent object with a linear power of about 500, the 

 ciliary action would be as readily demonstrated in this 

 species as in G. compressa, as the tessellated cells abound 

 on the inner surface of the interstitial cells to as great an 

 extent as they do in the last-named species. 



The pores of this sponge are so completely hidden by the 

 cone of defensive spicula that surrounds them that \ have 

 never succeeded in obtaining a view of them from the outer 

 surface, but under favorable circumstances, when a section 

 of one of the interstitial cells is made so as to allow of an 

 oblique view of the inside of its conical termination, they 

 are seen to occupy all parts of the cone, and are best 

 observed by the aid of a Lieberktihn and a power of about 

 150 linear; they are tolerably numerous, and I have seen 

 four in the space that would be occupied by one of the tri- 

 radiate spicula. The mechanism of the ciliary appendages 

 of the distal terminations of the interstitial cells is truly 

 simple and beautiful. 



In the dead specimens we find the ciliary appendages 

 usually closed ; the distal apices of the spicula are brought 



