2^4'^'*^ 



MEMOIR 



ON 



THE PEARLY NAUTILUS. 



J- HE true relations of every class of animals are now acknowledged to depend for 

 their development chiefly on anatomical investigation : and the necessity of this 

 mode of inquiry has been rendered more especially obvious with respect to those 

 tribes whose outward forms, being unsupported by any firm and resisting frame- 

 work, present in consequence variations extremely disproportionate to the dif- 

 ferences exhibited in habits and powers of action. In this division of animals 

 the most important and unexpected results have been obtained from the dis- 

 section of the Cephalopods, which, under a form approaching to that of the 

 Polype, disguise an organization as rich in the variety of parts, as it is peculiar 

 in their mode of arrangement. Hence they have afforded one of the strongest 

 arguments against the theory of the simple and unbroken series, for a long 

 time supposed to be the natural distribution of the animal kingdom : and they 

 have subsequently been deemed not less adverse to a more modern doctrine, 

 which, ascending to the consideration of the analogies presented in the ma- 

 terials of individual organisms, seeks to reduce their varied plans of compo- 

 sition to a principle of unity. 



The characteristic pecuUarity in the disposition of the organs of this remark- 

 able class has, indeed, been considered in some measure reconcileable to the 

 higher types ; and the advocates of the doctrine of M. Geoffroy St. Hilaire have 

 endeavoured to produce a semblance of conformity between the Cephalopoda 

 and the Vertebrata*. On the other hand, the Baron Cuvierf, whilst insisting 



* Geoffroy St. Hilaire, Principes de Philosophie Zoologique, 8vo, 1830, p. 35. 

 t Annales des Sciences Naturelks, xix. p. 241. 



B 



