BRITISH SPONGIAD^E. 221 



Some naturalists have conceived the idea that the per- 

 forations in the oyster-shells and in limestone rocks so 

 constantly occupied by the sponge, and those also inhabited 

 by lithodomus molluscs, were effected by the secretion, by 

 the animal of carbonic or other acids. The perforation of 

 sound hard wood by such molluscs, and that of a mass of 

 solid Highgate resin, in the British Museum, which still 

 contains the lithodomus shell that excavated it, could never 

 have been effected in the sea or out of it by such agents. 

 On the contrary of both these views, I have in my collection 

 several specimens of large Balani, which I took from the 

 sides of the rocks forming the Guliot Caves in Sark, which 

 are perforated, in the usual manner, with numerous sinuous 

 canals, which I found filled with the living Annelids, the 

 dried remains of which still remain in them, and without 

 the slightest indication of the presence of H. celata, and I 

 have also found living Annelids in the deeply-seated portions 

 of the perforations in the limestone boulders of Tenby, 

 beyond the range of the sponge ; so that I think it may be 

 reasonably concluded, that the sponge occupies the canals 

 and cavities in shells and stones that have been excavated 

 by other animals, and that they have no power to excavate 

 such residences themselves. 



Such speculative views regarding the habits and powers 

 of marine animals by inland and imaginative naturalists are 

 very apt to mislead the young student. A little close ob- 

 servation and accurate description at the proper localities, 

 is infinitely more valuable than a laborious closet treatise 

 on such subjects. 



Dr. Grant, I believe, gave no generic description of 

 Chona, and, in his account of it, stated that it was poly- 

 piferous. Dr. Johnston, after careful examination, not con- 

 sidering it to be a Zoophyte, referred it to its proper place 

 in the system of arrangement of the sponges that was then 

 received, as a Halichondria, and subsequently in the division 

 of that genus into numerous others, I have referred it to 

 the extensive genus Hymeniacidon. There can be no reason- 

 able doubt that had not Dr. Grant been misled by ac- 

 cidental circumstances, and thereby been induced to believe 



