344 Natural History of Molluscous Animals : — 
toothed and inflected, but plain and effuse. (fie. 88.) They 
8 are then, in fact, convolute shells 
of the ordinary chamactent and are 
obviously enlarged, like all others, 
by the addition of matter to the 
outer lip alone. But 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 Cypre’e are not the only mollusca 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 Mollisca strengthen the lips of their 
shell with an external or internal rib: others s 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. T hus, the Strombusidee (Str6mbus Zn.) 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 Fossil Shells. 
