344' Natural History of Molluscous Animals : — 



toothed and inflected, but plain and effuse. {Jig, 88.) They 

 ^® ^'^^fWf^'tm ^^^ then, in fact, convolute shells 



of the ordinary character, and are 

 obviously enlarged, like all others, 

 by the addition of matter to the 

 outer lip alone. fiut maturity 

 brings with it a change in the 

 organs of the animal. The lobes of its cloak become more 

 developed, and ultimately very large; so that, one issuing 

 from each side of the aperture, they can cover the shell, and 

 meet in the centre of the back. These lobes are secretory 

 organs, and pour out an abundance of lime in a vitreous 

 state ; and by their motions spreading it over the outer surface 

 the shell is thickened, and assumes a form totally different 

 from its primary one, and dependent on the new developement 

 of the soft parts. 



The Cypr<^^^ are not the only moUusca which acquire a 

 superior developement at maturity; but it is common, in a 

 greater or less degree, to many of them. At this period, 

 many land and marine Mollusca strengthen the lips of their 

 shell with an external or internal rib : others modify and con- 

 tract it with a deposition of vitreous lime ; and others, again, 

 enlarge it by the addition of parts of which there was no pre- 

 vious trace. Thus, the AStromb^sidse (A^trombus Lin.) resemble 

 a cone in their young state, and have no dilated and spinous 

 lip, so remarkably characteristic of their perfect shells. Here 

 we must suppose that, about this period, the lateral lobe of 

 the cloak is enlarged and otherwise changed, in accordance 

 with the digitations of the lip. 



It is here necessary to take some notice of an opinion, 

 which, though not, perhaps, originally proposed by him, has 

 of late been much insisted on by Mr. G. B. Sowerby, a na- 

 turalist who has paid particular attention to conchology, and 

 whose work *, from which I am about to quote, you will find 

 very useful in your future studies. He tells us that the ani- 

 mal of the cowries, of the cones, and of some other genera, 

 has the capability of dissolving and reabsorbing the calcareous 

 matter of one part of the shell, and of again depositing it in 

 places where additional strength or size is required by the 

 change of form which accompanies the progress towards ma- 

 turity. Thus he accounts for the fact that " young cowries 

 which have formed their involute outer lip, are generally 

 larger than when they are full grown and have completed 



* Genera of Recent and FossU Shells. 



