REPORT ON ZOOLOGY. 219 



any other groups placed higher in the system *. Mr. MacLeay 

 has endeavoured to show that in their general structure they 

 make the nearest approach to the Chelonian Reptiles f. He 

 allows, however, that the hiatus occurring between is very con- 

 siderable. M. Latreille, in a memoir published in 1 823 J, has 

 pointed out several resemblances between them and Fish, and 

 thinks that they show considerable affinity to the Rays and other 

 Cartilaginous Fishes. These resemblances refer exclusively to 

 the external structure of the two classes. More recently the Ce- 

 phalopoda have been much investigated by MM. Laurencet and 

 Meyraux. In a memoir read to the Royal Academy of Sciences 

 at Paris in 1830 §, these naturalists attempted to lessen the 

 gap that was supposed to exist between them and the Vertebrata, 

 in like manner as Geoflfroy had previously done with respect to 

 the gap between these last and the Anniilosa. They would de- 

 monstrate that the plan upon which the Cephalopoda are con- 

 structed does not depart so widely as was imagined from that of 

 the structure of the Vertebrata', that the same organs appear 

 in both groups, though somewhat modified and transposed ; and 

 that in order to make the structures conformable, we are only 

 to suppose a vertebrate animal doubled back upon itself, when 

 the relative position of the several organs in this last will be 

 essentially the same as in a Cephalopod. Geoffroy, in his report 

 on this memoir to the French Academy, took occasion to ob- 

 serve how favourable the results at which these anatomists had 

 arrived were to his peculiar views respecting the unity of com- 

 position in the animal kingdom. Cuvier, who was opposed to 

 these views, replied to Geoffroy ; and for some time after a sharp 

 controversy was kept up between these two distinguished natu- 

 ralists on this subject. To state the several memoirs, and verbal 

 communications to the Royal Academy of Sciences, which 

 arose on both sides of this question, would lead us too far from 

 the present subject || . We may mention, however, one memoir 

 by Cuvier, in which he states, with reference to the singular 

 opinion advanced by Laurencet and Meyraux, the results of a 

 rigid comparison which he actually made between a Cephalopod 

 and a Vertebrate Animal doubled back in the manner they di- 



* Mem. sur les Ccphalop., 8fC., p. 43. f Hor. Ent., p. 254 to 258. 



X Mem. de la Soc. d'Hist. Nat. de Paris, torn. i. p. 269. 



§ Quelques Considerations sur l' Organisation des MoUusques. I am ignorant 

 as to whether this memoir has heen hitherto published. 



II Geoffroy 's memoirs were afterwards collected by himself into one volume, 

 and published under the following title : Principes de Philosophie Zoologique, 

 discutis en Mars 1830, au sein de I' Acad. Roy. des Sciences. Par. 1830, 8vo. 

 Cuvier also expressed a determination to publish his under the title of De la 

 Variete de Composition des Animaux, I am not aware, however, that these 

 last ever appeared. 



