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XIX. — On the Structure of the Shells of Molluscous and Conchife- 

 rous Animals. By J. S. Bowerbank, Esq., F.R.S., &c. 



Read January 18, and November 15, 1843. 



The results arising from an examination of the organic tissues of 

 the Corallidae, published in the * Philosophical Transactions,' part 2, 

 1842, p. 215, suggested to me the idea of pursuing a similar course 

 of researches into the nature and origin of the testaceous coverings 

 of molluscous and conchiferous animals, in the hope of being able, in 

 some slight degree, to add to the present amount of knowledge of the 

 origin and development of these curious animal structures. The ex- 

 istence of organic cells and vessels in the tissues of the Spongiadae, 

 and in the bony skeletons of the Corallidae, naturally induced a be- 

 lief that in the testaceous coverings of the still higher classes of or- 

 ganized beings, these primary organic tissues would be developed in 

 a more marked and determined form, and that it might eventually 

 prove that the ingenious doctrine of the origin and mode of increase 

 of shells, — first promulgated by Reaumur, and adopted by a great 

 majority of subsequent naturalists up to the present time, — would be 

 found in some degree incorrect, and that instead of being excremen- 

 titious, unorganized and crystallized bodies, we should find the origin 

 of these parts of the animal, and their mode of increment, to be in 

 accordance with those laws of vital origin and increase which are so 

 beautifully developed, by the aid of the microscope, in the bony ske- 

 letons of animals both above and below them in the chain of created 

 beings. With these views I commenced my researches, early in the 

 spring of 1842, by a careful examination of the young cartilaginous 

 lips of the common garden-snail (Helix aspersa), and subsequently 

 by an examination of the structures of numerous species of adult 

 univalve and bivalve shells, by maceration in weak solutions of hy- 

 drochloric acid, and by other modes. I will not trespass upon the 

 patience of my readers by entering upon a minute detail of the facts 

 arising out of each of these examinations, but confine myself to a 

 description of the general results arising from them. 



Reaumur, and subsequent writers upon this subject, entertained the 

 idea that the periodical additions to the lips of the shells of land- 

 snails were effected at the will of the animal in the following manner. 

 In the first place, the snail caused an exudation of a thin stratum of 

 coagulable lymph from the surface of its mantle, which, being united 



