86 ESriRODUCTION. 



limits. The second division is cliaractemed in a much 

 less positive manner. It embraces beings of very vari- 

 ous structure, possessing but few characteristics in com- 

 mon, and created on plans of organization so widely 

 different, that nothing brings them together in the same 

 group except the negative quality of wanting those 

 properties which distinguish the first. In some of 

 them, the nervous system remains undiscovered, and 

 if it exists, is less developed than in the ganglionary 

 animals. This classification, wliich is not altogether 

 philosophical, is therefore liable to be re-modelled, as 

 the progress of knowledge shall require it, and may be 

 said to be, at present, in a rather unsettled state. 

 Various propositions have been made by different 

 naturalists, each influenced by his peculiar theoretical 

 views, for its subdivision into natural classes, but none 

 of these have met with general acceptation. It is 

 certain, however, that the Invertehrata vrill be recognized 

 to contain several distinct divisions, each holding a rank 

 equally as independent as the vertebrate animals, dis- 

 tinguished by a principle of conformation equally definite, 

 and removed to a greater or less distance from them, 

 according to the perfection of the structure and func- 

 tions of the animals contained in it. 



The order and system impressed by the Divine Will 

 on all created thuigs, indicated to the early philosophers, 

 as clearly as to those of our own time, that some princi- 

 ple of arrangement must prevail in the constitution of 

 animated beings ; and hence their attention was given 



