THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



No. 79. DECEMBER 1843. 



XLVI. — General results of Mia-oscopic Inquiries into the Minute 

 Structure of the Skeletons of Mollusca, Crustacea and Echino- 

 dermata. By William B. Carpenter, M.D.* 

 [With two Plates.] 

 Having been engaged, during the last eighteen months, in mi- 

 croscopic researches into the skeletons or hard parts of animals, 

 and having had my attention particidarly chrected towards the 

 shells of Mollusca and Crustacea, and to the shells, spines, stems, 

 &c. of the Echinodermata, I have been led to believe that a short 

 resume of the results at which I have arrived, would be interest- 

 ing to the members of the Geological Section of the British As- 

 sociation, and might prove of importance in giving a stimulus to 

 further inquiry. Were it not, indeed, in the hope that the ad- 

 vance of science might be promoted by my bringing forward these 

 results in their present form, I should have hesitated in doing 

 so, until they had attained more completeness. I shall com- 

 mence with the ^lollusca, as presenting the greatest number of 

 points of interest. 



Mollusca. 

 The first point on which I desire to lay stress, is the complete 

 distinctness of the organic basis of the shells of Mollusca from 

 the calcareous portion. The two are not uniformly diffused 

 through the shell, as some have sujiposed, but are separate ele- 

 ments, each having its own place. The organic or animal basis 

 presents very definite characters, by which its nature may be de- 

 termined, when the calcareous portion has been removed by the 

 action of an acid. 



I also think it desii'able to state, in limine, that the structure 

 of all shells appears to me to be equally crystalline ; the carbonate 

 of lime uniformly presenting a crystalline arrangement, if not a 

 regular form. I cannot admit, therefore, the distinction between 

 the crystalline and concretionary shells which ls\x. Gray has at- 

 tempted to establish ; nor can I recognise the two forms of ciy- 



* Read to the Geological Section of the British Association, August 1843; 

 and comnuinicated by tlie Autlior. 



Ann. ^' Mag. N. Hist. Vol. xii. 2 D 



