39 



stances of its nature, secrete a new shell from all parts of the body at once, 

 and with all the different phases of colour exhibited in early growth, when 

 it has reached to an advanced condition of its existence ? " 



The animal does not appear to quit the shell, as Lamarck supposed, but 

 dissolves the outer portion with its acetose juices. All visible trace of the 

 shell maybe 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 powder which furnishes the adult with its last 

 coating of enamel can be exerted to the formation of as many superincum- 

 bent layers as may be necessary to replace all that has been decomposed. 

 That a dissolution takes place there can be no doubt : — " the shell gra- 

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

 duller in colour, and finally disappears;" a circumstance which maybe 

 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 P/iolades, and other terebrating mollusks, exercise a power of 

 absorbing which enables them to penetrate the hardest limestone rock. 

 The microscopical structure of the Cowrey 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 to so highly a polished 

 state of enamel, when 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 a 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, but is of the wide, ventricose shape of a Cgrnba, and rapidly consoli- 

 dates into the adult shell. 



With these generalizations I think it may be assumed that the Cowrey 

 possesses, upon an emergency, 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 accom- 

 plished 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 

 winch only happens under peculiar conditions. 



In most species of Cypraa three separate phases of colour may be defined 

 at different periods of growth. In the C. Mauritiana, for example, the 

 colour of its first state, or Bulla form, is a pale yellow, over which the ful- 

 vous brown spreads in bands of waves ; in an intermediate state the waves 

 become agglomerated, and leave the yellow in triangular flame-like spots ; 

 and when the teeth are fully developed, the sides become thickened with a 



