376 Mr. L. Reeve on the Re-caJcification of the Shell in Cyprjea. 



The animal does not quit the shell as Lamarck supposed, but dis- 

 solves the outer portion with its acetous juices. All visible trace 

 of the shell may be thus removed without weakening M. Deshayes^ 

 proposition, founded on the circumstance of the mantle being the 

 only organ charged with the secretive fluid. The mantle is always 

 capable of extension over the shell ; and the same power which 

 furnishes the adult with its last coating of enamel can be exerted 

 to the formation of as many superincumbent layers as maybe 

 necessary to replace all that has been decomposed. That a dis- 

 solution takes place there can be no doubt ; the shell gradually 

 swells, says Lieut. Hankey, and cracks, becomes thinner and 

 duller in colour, and finally disappears ; a circumstance which 

 may be easily credited when it is remembered that the Murex 

 possesses the faculty of removing spines, or any similar obstacles 

 to its advancement of growth, and that the Pholades and other 

 terebrating mollusks exercise a power of absorbing which enables 

 them to penetrate the hardest limestone rocks. The microscopical 

 structure of the Cowry shell is, moreover, of a nature peculiarly 

 tenacious of absorption ; it is composed of a large quantity of 

 carbonate of lime in proportion to the amount of membranous 

 substance ; and this accounts for its surface becoming vitrified, 

 as it were, to such a highly polished state of enamel, in contact 

 with the acidity of the soft parts. 



There is another circumstance in Lieut. Hankey^s narrative to 

 which attention should be given, respecting the formation of the 

 new shell : — the glutinous matter which has the appearance of 

 shell-lac, and is so fragile that it yields to the touch, does not 

 assume the narrow cylindrical Bulla form, — it does not follow the 

 original plan of revolving round a columellar axis, but is of the 

 wide ventricose shape of a Cymha, and rapidly consolidates into 

 the adult shell. 



With these generalizations I think it may be assumed that 

 the Cypraa possesses the faculty of decomposing, during one or 

 more periods of its existence, any portion of the shell that is 

 liable to resist its advancement of growth ; that the renewal of 

 the shell is accomplished within a comparatively short space of 

 time ; and that the columella with its internal spiral partitions 

 remains undisturbed. It may, however, be inferred that it is an 

 operation of extremely rare occurrence, and one which only hap- 

 pens under peculiar conditions. 



Note. 



Since writing the above, I have observed that Mr. Gray's opi- 

 nion on the subject at the time of the publication of his " Mono- 

 graph on the Cyprmdea '' ran as follows : — 



" In this family I have often observed full-grown specimens of 



