DESULTORY SKETCHES IN NATURAL HISTORY. 45 



tion, has been supposed to be afforded by certain of the higher Ce- 

 phalopods, as the Cuttles, which internally deposit a quantity of 

 earthy matter (the well-known cuttle-Jish hone of commerce). But 

 it should be borne in mind that the establishment of these leading 

 divisions of the animal kingdom reposes ultimately on the nervous 

 system, the confluent masses of which are disposed altogether dif- 

 ferently in the Vertebrata and Mollusca ; and that, in this most 

 important and influential portion of their organization, both the 

 Cyclostomata and Cephalopoda rigidly conform to their respective 

 sub-regnal models of formation, the former merely presenting what 

 is comparatively termed an arrested development, the latter a more 

 complete development than usual. The distribution of the princi- 

 pal aggregations of neurine, or nervous proximate element essential 

 and peculiar to animal organization, thus determines apart the three 

 divisions of Vertebrata, Mollusca, and Articulata, with unerring cer- 

 titude ; and it remains to be shown that in this fundamental charac- 

 ter, to which all others are subservient, a transition from one to 

 another of these primary sub-types of form, or an intermediate or- 

 ganism, exists in any one instance : but we do not attach the same 

 importance to those simply positive and negative characters upon 

 which physiologists have hitherto attempted to dismember the Ra- 

 diata of Cuvier into analogous divisions, if only because they do 

 pass into each other, as might be predicated from the nature of the 

 difference ; their distinction consisting merely in the degrees of de~ 

 velopment traceable in several different minor groups, from the 

 diffusion of the various proximate elements of the body in a homo- 

 geneous pulp, to their gradual separation into tissues more or less 

 discernible. Analogy with the three first great divisions should 

 indicate that if equivalent types of form exist among the Radiata, 

 their integrity would be as constantly maintained in every species 

 respectively framed upon them. 



We may, indeed, fairly waive the consideration of the miscella- 

 neous assemblage of beings of inferior organization, provisionally 

 brought together under the term Radiata, if the position for which 

 we strenuously contend can be satisfactorily established with respect 

 to the three higher grand divisions of the animal kingdom, the mu- 

 tual relations of the component members of xvhich are tolerably un- 

 derstood; and proceed next to remark that neither of the four 

 classes into which the Vertebrata are divided grade into each other, 

 any more than those superior groups on which we have been com- 

 menting, each being distinct in itself, so that no one species is 

 referred to either of them with the slightest hesitation ; or if, in 



