Natural History of Molluscous Atiimals. '595 



Akt. IX. 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 Shelly and 

 on t/teir Loco7notion. 



Towards 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 snaiPs 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, and to 

 remove, from time to time, the particles of the shell ? " f 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. 

 -}- Cemp. Anatomy, vol. i. p. 119. trans. 

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