hi Organized Beings. 99 



vertebrata the types which it presents in the other two great 

 divisions of the animal kingdom where it is distinctly marked, 

 each of the other systems of the vertebrata is, I think, deve- 

 loped upon a single uniform plan. Thus we should not be led 

 to look in insects with any analogies with their nutritive system, 

 nor among the moUusca for any representation of their locomo- 

 tive organs. The whole structure of the typical mollusca is de- 

 voted to the perfection of their nutritive system, and we conse- 

 quently find, an asymmetrical development prevailing through- 

 out, involving (except in the highest cephalopodes) even their 

 organs of locomotion ; and we fully recognize this asymmetrical 

 form in the structure of the thoracic and abdominal viscera of 

 the vertebrata in general. In the articulata, on the other 

 hand, where the functions of animal life so greatly predominate, 

 symmetrical development of the organs of locomotion is the 

 prevailing character ; and the form of the nutritive system is 

 made partly to yield to this. This symmetrical development 

 is everywhere characteristic of the organs of animal life in the 

 vertebrata ; and the resemblance forcibly occurs to us between 

 the subdivisions of these organs in the vertebrata and the higher 

 articulata, keeping, however, this great principle in view, that 

 in the former, the organs of support are in part of the neiiro- 

 skeleton, whilst in the latter these are formed by the dermo- 

 sTieleton. It appears to me, therefore, that in the study of each 

 division of the animal kingdom, we shall find parts analogous 

 to the rest, and that the sum-total of the effect is produced by 

 the proportional development of each system, which would 

 seem, therefore, finally resolvable into a question of degree only. 

 It by no means follows, however, from this doctrine, that the 

 whole animal kingdom is formed upon the same type, and pro- 

 gressively developed in such a manner that the transitory 

 states of the higher animals furnish exact representations of 

 the permanent forms of the lower. What is meant to be main- 

 tained is, that each organ in the progress of its evolution pre- 

 sents analogies in elementary structure and in degree of deve- 

 lopment (by no means necessarily in external form) with the 

 permanent states of the same in the classes beneath ; and this 

 is again to be understood with the limitation just now expressed, 

 which will prevent us from seeking in insects any forms analo- 



