360 TOILERS IN THE SEA. 



of the grounds upon which he attributed their forma- 

 tion to the sponges themselves. "The boring sponges, 

 as far as I have examined them, are branched, or are 

 composed of lobes united by delicate stems, and all 

 more or less anastomose, according to the species ; 

 many of them are beautifully arborescent, and of 

 great delicacy. They all bury themselves in shells, 

 or other calcareous bodies, and communicate with 

 the water by papillae, or oscula, protruding through 

 circular holes, in the surface of the containing sub- 

 stance or matrix. In dead shells the papillae pass 

 through both surfaces, but in living ones rarely 

 penetrate the innermost layer, though occasionally 

 they do so. When a mollusk is thus wounded, it 

 deposits calcareous matter over the orifice, and 

 generally succeeds in excluding the intruder. The 

 species vary considerably in form, and might be 

 divided into two or three distinct groups. In some, 

 the branches are almost linear, and anastomose only 

 to a very slight degree, others form a complete 

 network, with the meshes so small that very little of 

 the matrix remains between the branches ; some have 

 the branches moderately lobed, and others, again, 

 have the lobes large, and crowded upon each other in 

 all directions, and united by fine, very short stems. In 

 most the terminal twigs are very minute, and exhibit 

 in. a decided manner the mode of growth (fig. 70)." 

 He then details the peculiarities in different species, 



