XVII 



ON THE MORPHOLOGY OF THE CEPHALOUS 



MOLLUSCA, AS ILLUSTRATED BY THE ANATOMY 



OF CERTAIN HETEROPODA AND PTEROPODA 



COLLECTED DURING THE VOYAGE OF 



H.M.S. RATTLESNAKE IN 1846-50 



Philosophical Transactions of the Royal Society, vol. cxliii. 1853,//. \,pp. 29-66 



" The mere description of appearances even of the interior structure, 

 still less of the exterior surface of an animal, without the deductions 

 which they legitimately yield, is of comparatively small value to the 

 philosophic naturalist ; for of what value are facts until they have been 

 made subservient to establishing general conclusions and laws of cor- 

 relation, by which the judgment may be safely guided in regard to 

 future glimpses at new phenomena in nature ? ' ^ 



If I prefix this admirable exposition of the true aims of anatomical 

 investigation to the present essay, it is that I may justif)', by the 

 highest authority, the course which I have taken in considering what 

 of new facts it contains, as of subordinate importance to the reasonings 

 which may be based upon those facts ; in making its scope more mor- 

 phological than zoological. 



The morphology of the Cephalous Mollusca is a subject which has 

 been greatly neglected. No Savigny has determined the homologies 

 of their different organs, and so furnished the only scientific basis for 

 anatomical and zoological nomenclature. 



It is not settled whether the back of a cuttle-fish answers to the 

 dorsal or to the ventral surface of a Gasteropod. It is not decided 

 whether the arms and funnel of the one have or have not their homo- 

 logues in the other. The dorsal integument of a Doris and the cloak 

 of a Whelk are both called " mantle," without any e\-idence to show 

 that they are really homologous. 



Nor do very much more definite notions seem to have prevailed 



^ Owen, Anatomy o{ Spirilla, Voyage of Samarang, Zoology, p. 12. 



