Natural History of Molluscous Animals. 525 
Art. 1X. An Introduction to the Natural History of Molluscous 
Animals. In a Series of Letters. By G. J. 
Letter 6. On the Connection between the Animal and Shell, ed 
on their Locomotion. 
‘Towarps the conclusion of my last letter, I said that the 
shell was to be considered as a dead or inorganic substance ; 
by which I meant that there was no vascular connection 
between it and the animal, and no internal circulation in the 
former by which its figure can be altered or its injuries 
repaired. This is admitted by all; but, notwithstanding, 
there are naturalists who maintain that the shell is not dead 
so long as it remains in connection with the living animal. 
Its vitality, says Dr. Fleming *, is demonstrated from the 
changes which it undergoes when detached: the plates of 
animal matter harden ; the epidermis dries, cracks, and falls 
off; and in many cases the colours fade, or disappear. And 
what but vitality could have prevented these changes pre- 
viously ? ‘There is, perhaps, some fallacy in the observations ; 
for these effects of chemical and mechanical agents often begin 
their work before the snail’s death, perhaps always, if that 
death has not been premature. ‘The epidermis of old shells is 
worn off more or less; their colours are frequently less vivid, 
unless when polished or renewed by expansions of the fleshy 
cloak ; and parts of them are almost always destroyed or 
worn down. If the agents act more powerfully subsequently 
to death, it is because ‘they are applied in circumstances more 
favourable to their operation. Cuvier and Blumenbach favour 
the same opinion, because “ the oyster and muscle adhere to 
the shell, not only by their muscles, but by the whole border 
of their cloak;” and because ‘ the oyster has always be- 
tween the two last strata of the convex valve a considerable 
vacuity, which is filled with a fetid acrid liquor, and which 
communicates with the interior of the body by a particular 
aperture. How,” asks Cuvier, “is this vacuity produced ? and, 
above all, how is it removed upon the formation of each new 
stratum, if the arterial and absorbent vessels do not penetrate 
into the centre of the strata, to regulate its position, ahd to 
remove, from time to time, the particles of the shell?” + In 
answer to this I would reply, that the connection between 
the shell and the cloak of the muscle, although so very close 
that some degree of force is requisite to separate them, is 
nevertheless one only of contact, as I infer from the circum. 
* Phil. of Zoology, vol. ii. p. 405. 
+ Comp. Anatomy, vol. i. p. 119. trans. 
MM 3 
