J. G. WALLER ON THE BURROWING SPONGE. 271 



of Natural History/ attributes their excavating power to trie pre- 

 sence of a multitude of minute siliceous crystalline particles ad- 

 hering to the substance of the sponge ; these, he supposes, to be set 

 in motion by some means analogous to ciliary action. In what- 

 ever way this action may be produced, however, there can be no 

 doubt that these sponges are constantly and silently effecting the 

 disintegration of submarine calcareous bodies, the shelly cover- 

 ing, it may be, of animals far higher in organization than 

 they ; nay, in many instances, they prove themselves formidable 

 enemies even to living mollusca, by boring completely through the 

 shell. In this case the animal whose domicile is so uncere- 

 moniously invaded has no alternative but to raise a wall of new 

 shelly matter between himself and his unwelcome guest, and in 

 this manner generally succeeds at last in barring him out. — Vide 

 Hogg on the Microscope,' pp. 285, 286." 



It would not be difficult to criticize this passage, in which a series 

 of assumptions are treated as conclusions, and in which there is 

 really no evidence whatever. But it is fair to the writer to say that, 

 he only repeats what another has advanced, and which he finds to 

 be generally accepted. Before I enter into the general subject, 

 some account of the scientific history of this organism is required. 



Its discovery is due to Dr. Grant, a name always to be spoken of 

 with respect. He found it protruding from orifices in an oyster 

 shell, and on touching it with a needle it retracted, and withdrew 

 within the aperture. He considered it to be a zoophyte, and named 

 it " Cliona Celata." Dr. Johnston brought it into its proper place 

 amongst the family of sponges, calling it " Halichondrin Celata." 

 Then comes another observer, Mr. Hancock, who, in a most elabo- 

 rate and interesting article in the " Annals and Magazine of Natural 

 History," N.S. vol. iii., p. 332, &c, first pronounces it to be a 

 " boring or burrowing sponge," and divides it into twelve species. In 

 this article he candidly admits, that the prevalent opinion then was, 

 that the sponge did not excavate the burrows in which it lived, but 

 that those were the work of worms. This view, however, he com- 

 bats strenuously, as he says, " were this belief correct, the chambers 

 would occasionally occur only partially occupied. This never hap- 

 pens." Now, " this never " is unlucky. It does so happen that 

 the excavations are not always filled, on the contrary are often 

 entirely empty, and sometimes only partially occupied. On this 

 point I have abundant evidence. I have recently seen oyster shells 



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