with descriptions of neiv Species. 329 



tial in determining that of the chambers it inhabits. The test 

 then can be easily apphed; and were the secretion of an acid nature, 

 there could be little difficulty, one would think, in detecting it ; 

 particularly as Cliona appears to work perpetually — at least so 

 long as it continues to grow. • I have completely failed, however, 

 in detecting an acid. 



I took C. gorgonioides alive fresh from the sea, and breaking 

 up the stone in which it was lodged removed the creature by 

 piecemeal, and placing each portion on litmus-paper pressed 

 the fluids out of it between plates of glass ; but not the slightest 

 alteration occurred. I continued trying piece after piece for 

 several hours, and contrived to remove portions of the animal 

 with the sui'face entire ; but all was in vain, — no indications of 

 an acid solvent could be obtained. 



In a specimen of the Strombus gigas in the Newcastle Museum 

 penetrated by a species of Cliona, the papillae have passed through 

 the strong horny epidermis, drilling it with great precision ; the 

 holes are quite circular, and of the same size as those in the shell. 

 This could hardly be achieved by an acid solvent. 



When a portion of the fresh C celata is carefully removed 

 from the chambers and placed in a little acetic acid, a distinct 

 effervescence takes place as if calcareous matter mingled with the 

 tissue. The same result occurs when a little of the dried sub- 

 stance adhering to the sides of the excavations of Thoosa is re- 

 moved and treated with the same acid. From these facts we 

 may conclude, perhaps, that no acid solvent had been employed ; 

 while it is likely, were the excavations effected by mechanical 

 means, that the surface and tissue would be charged with cal- 

 careous particles. Indeed such particles may generally be ob- 

 served strewed along the branched channels in the shell of the 

 oyster when inhabited by C. celata. I have also seen similar 

 calcareous particles adhering to the animal of C. gorgonioides 

 when removed from its chambers in limestone. These particles 

 are large enough to be detected with a pocket lens, and 

 will be more fully described further on. At present they are 

 alluded to, as they afford a pretty strong proof of mechanical 

 agency. 



The excavations wovdd then appear to be effected by mechanical, 

 and not by chemical means. What is the instrument, and how 

 is it applied ? 



With respect to Cliona, it is well known to possess siliceous 

 spicula ; some of the points of which penetrate the surface of 

 the animal, and might be supposed capable of reducing the cal- 

 careous bodies in which these creatures bury themselves. But 

 other and apparently more efficient agents have been discovered, 

 covering the surface of the sponge. 



