CHABACTEES OF VERTEBRATE ASTMAL: 



Ix the numerous classes of animals which constituted that inferior, 

 more extensive, and diversified group, linked together by the single 

 negative character of the absence of a vertebral column, and thence 

 termed '•' Invertebrata," we saw that, as the several series became ele- 

 vated in the scale of organisation, thev diverged from one another by 

 reason of the preponderating development of some particular cia5s of 

 organs, and culminated in species, inferior either in their general form, 

 or their powers of motion and perception, to some of the antec-edent 

 forms, through which the series had passed.* The spider and the crab 

 are not the kinds of animals in which one should have anticipated 

 that the type of organisation^ so richly varied in the Insect class, would 

 have ended, had that class been a step in the direct progress to the 

 vertebrate series. The loss of wings,, and the abrogation of the power 

 of flight, would indicate a retrograde course of development. In the in- 

 sect, the animal organs, more particularly those of locomotion, prepon- 

 derate over the v^etative or plastic organs, and in the attempt, as it 

 were, to restore the balance, by establishing, as in the Crustacea and 

 Arachnida, a better defined system of circulation, and a more vigorotis 

 and concentrated heart, the general plan of the articulate structure 

 appears not to be such as to bear this adjustment without a sacrifice 

 of some of the faculties enjoyed by Insects. So likewise the route of 

 organisation traceable through the molluscous type seems, on the 

 other hand, to lead to an extreme subordination of the motive and 

 sensitive to the vegetative systems. And in those species which make 

 the nearest approach to the Tertebrata. we find the viscera of organic 

 life occupying so large a proportion of the body, that no rc>om is left 

 for the development of nervous or muscular organs, except by what 

 seems an undue expansion and overloading of the head, as, for ex- 

 ample, in the Cephalopoda. In fact, the nervous system, the essence 

 and prime distinction of the animaL had not, so to speak, any proper 

 or defined abode in the bodies of the invertebrated animals. Its 

 centres were sometimes dispersed irregularly through the general 

 cavity of the body, sometimes aggregated around the gullet, some- 

 times arranged with more symmetry along the abdomen : yet seldom 

 better cared for or protected than the neighbouring viscera. 



The grand modification, by which a higher type of organisation is 

 established, and one which becomes finally equal to all the contin- 

 gencies, powers, and offices of animated beings, in relation to this 

 ^^•^net, is the allocation of the mysterious albuminous electric pulp in 

 a special cylindrical cavity, of which the firm walls rest upon a basal 



* Hunteriau Lectures, Invertebrata. Sto. IS43. 



