272 Mr Osier on Burrowing and Boring 



supports the presumptions to be collected from these data by 

 the fact, that many naked animals of the softest texture form 

 their habitations in limestone. The boring Annelides, he re- 

 marks, are innumerable in calcareous rocks, and are found to 

 attack every marine shell, almost as soon as it has acquired 

 sufficient thickness to afford them a nidus ; and he illustrates 

 this observation by reference to the oyster-shells, so often found 

 on the coasts, completely perforated, and occupied by " a kind of 

 sponge" — " a fibrous yellow pulp, filling a number of irregular 

 cells.'" * " The penetration of these naked animals (says Mr 

 Osier) leads irresistibly to the conclusion, that a shell is not 

 essential to the boring process ; and it would be inconsistent 

 with the simplicity observable in every part of nature, to sup- 

 pose that she has provided such different means for accomplish- 

 ing the same end." 



But the theory of a solvent, Mr Osier states, does not rest 

 on mere negative proof. It appears impossible to explain on 

 any other grounds the animal's exclusive choice of calcareous 

 matter; a choice evidently depending on its inability to penetrate 

 stones of a different nature. In specimens where portions of 

 silex have projected into their holes, their progress has been 

 found to be stopped from this cause. Where the Saxicavae 

 are abundant, and their holes communicating, the shells of 

 some are found to be acted on when exposed to the foot of 

 others ; and when the shell is penetrated the breach becomes 

 filled, not with new shelly matter, but with a firm yellow sub- 

 stance, insoluble in a strong mineral acid. A peculiar provision 

 is thus given to the animal to preserve it from destruction by 

 an injury to which it is particularly exposed ; and it would be 

 difficult, Mr Osier thinks, to conceive a fact short of absolute 



* Dr R. E. Grant of Edinburgh, in a paper in the Edin. New Philosophi- 

 cal Journal, October 1826, has ascertained that this " fibrous yellow pulp" 

 is a distinct and well-marked zoophyte, of which he gives an interesting 

 description, and arranges as a distinct genus, forming the connecting link 

 between the Alcyonium and the Sponge, under the name of Cliona celata. 

 The projecting tubular papillae of this animal, contrary to what Mr Osier 

 supposes, are distinctly irritable ; and Dr Grant even questions " whether 

 the sharp siliceous spicula, and the constant currents of its papillae, do not 

 exert some influence in forming or enlarging the habitation of this zoc- 

 pbyte." 



