REPORTS 



ON 



THE STATE OF SCIENCE. 



On the Microscopic Structure of Shells. By W. CarpenteRj M.D., 



F.R.S. 



I. Introductory/ Remarks. 

 I HAVE in vain searched the works of recent Conchological writers, for any 

 indication that Shell has any claim to the title of an organic structure. The 

 researches of Reaumur and Hatchett appear to have induced the universal 

 belief, that shell is an inorganic exudation from the surface of the mantle, 

 consisting of calcareous particles held together by a sort of animal glue. It 

 seems to have been formerly maintained by Herissant, however, that shell has 

 an organic structure, and that it grows by interstitial deposit in the manner of 

 bone. I have not been able, however, to find his original paper ; and only 

 make this statement on the authority of a reference which I have found to it 

 in the article Conchjliologie in the ' Encyclopedic Methodique,' in which he is 

 quoted as having endeavoured (but failed) to establish by " les experiences 

 ingenieuses, bien plus que solides," that shells grow by intus-susception, in- 

 stead of by accretion, as demonstrated by Reaumur. In this doctrine he was 

 undoubtedly wrong, as I shall hereafter show ; since, although all shell pos- 

 sesses a more or less definite organic structure, this structure rather cor- 

 responds with that of the various Epidermic appendages of Vertebrated 

 animals, than with that of their internal vascular skeleton ; and its mode of 

 growth must therefore be analogous rather to that of the former than to that 

 of the latter. 



The idea that such would be probably found to be the case, I expressed in 

 the second edition of my ' Principles of General and Comparative Physio- 

 logy' (October 184-1), as follows : — " The dense calcareous shells of the Mol- 

 lusca, and the thinner jointed envelopes of the Crustacea, have been com- 

 monly regarded as mere exudations of stony matter, mixed with an animal 

 glue secreted from the membrane which answers to the true skin. The hard 

 axes and sheaths of the Polypifera, however, have been also regarded in the 

 same light ; and yet, as will hereafter appear, these are unquestionably formed 

 by the consolidation of what was once living tissue*. From the analogy 

 which the shells of Mollusca and Crustacea bear to the epidermic appendages 

 of higher animals, there would seem reason to believe that the former, like 

 the latter, have their origin in cells, and that these are afterwards hardened 

 by the deposition of earthy matter in their interior." — (§ 44.) 



Acting upon this view, I commenced, in the spring of 1842, a series of in- 



* Reference was here made to the researches of M. Mihie-Edwards, upon the development 

 and growth of some of the corals. The natxu-e of their organic structnre has been subse- 

 quently elucidated with great success by Mr. Bowerbank. — (Pliil, Trans. 1842.) 

 1844. B 



