STRUCTURE OF SHELLS. 393 



has discovered in shell, but also by the phenomena which 

 occur in its reparation of injuries, whether that injury is 

 limited to the periostracum or inflicted on the substance 

 of the shell itself; for this reparation is not made by a 

 coat of calcareous matter spread over the wound by the 

 collar or mantle of the animal, as has been maintained, but 

 by an effusion of coagulable lymph in which cytoblasts are 

 produced in the first instance, and quickly succeeded by a 

 cellular structure, in which the earthy basis of the shell is 

 secreted, and by which the scar is filled up, or the fracture 

 cemented together,* 



Dr. W. B. Carpenter entered simultaneously with Mr. 

 Bowerbank on the investigation into the structure of shells, 

 but as his objects were different, he was led to work after a 

 more systematic fashion. Dr. Carpenter's principal object 

 appears to have been to discover whether the microscopic 

 structure of the shell was so peculiar and distinctive that 

 from it we might conclude as to its genus or family, so that 

 henceforth the conchologist, from an inspection of even a 

 fragment of a valve or whorl, might rival the zoologist in 

 conjuring up, on fixed principles, the image and character 

 of a beast of whose existence he is only made aware by a few 

 fragmentary remains. And Dr. Carpenter has been emi- 

 nently successful so far as the bivalve shells are concerned ; 

 for there is too much sameness in the structure of univalves 

 to give the same satisfactory results. This eminent physio- 

 logist has ascertained that an uniform structure prevails 

 throughout every part of a shell, and, consequently, that 

 the examination of but a very small piece suffices to deter- 

 mine its entire structure ; and he has also ascertained that 

 the species of the same genus present essentially a oneness 

 in pattern, so that any material deviation from it indicates 

 a family or generic difference in the structure of the ani- 

 mal. The conchologist who formerly broke the shell that 

 he was quarrying from its ancient tomb, lost his labour and 

 the key to the knowledge it might have disclosed to him ; 

 but now, if the shell be a bivalve, he has only to prepare a 

 fragment of his shattered document, and the key is recovered 

 that locked up in secrecy the world's former tenantry. 

 Such is one result of Dr. Carpenter's curious researches ; 

 but in proving it he has necessarily discovered many im- 

 portant facts bearing on the subjects of this letter. 



Dr. Carpenter concludes with Mr. Bowerbank, that all 



* Observations on the Structure of tlic Shells of Molluscous and Conchi- 

 ferous Animals, by J. S. Bowerbank, F.R.S., &c, published in the Trans- 

 actions of the Microscopical Society, vol. i. 123. Lond. L844. 



