BRANCHES OF THE ANIMAL KINGDOM. 217 



to say below about classes and orders, it will appear more 

 fully that it is important to make a distinction between 

 the plan of structure and the manner in which that 

 plan is carried out, or the degrees of. its complication and 

 its relative perfection or simplicity. But even after it is 

 understood that the plan of structure should be the lead- 

 ing characteristic of these primary groups, it does not yet 

 follow, without further examination, that the four great 

 branches of the animal kingdom, first distinguished by 

 Cuvier, are to be considered as the primary divisions 

 which Nature points out as fundamental. It will still be 

 necessary, by a careful and thorough investigation of the 

 subject, to ascertain what these primary groups are ; but 

 we shall have gained one point with reference to our 

 systems, that, whatever these primary groups, founded 

 upon different plans, which exist in nature, may be, when 

 they are once defined, or whilst they are admitted as the 

 temporary expression of our present knowledge, they 

 should be called the branches of the animal kingdom, 

 whether they be the Vertebrata, Articulata, Mollusca., and 

 Radiata of Cuvier, or the Artiozoaria, Actinozoaria, and 

 Amorphozoaria of Blainville, or the Vertebrata and Inver- 

 tebrata of Lamarck. The special inquiry into this point 

 must be left for a special paper. I will only add, that I 

 am daily more satisfied, that, in their general outlines, the 

 primary divisions of Cuvier are true to nature, and that 

 never did a naturalist exhibit a clearer and deeper insight 

 into the most general relations of animals than Cuvier, 

 when he perceived, not only that these primary groups are 

 founded upon differences in the plan of their structure, 

 but also how they are essentially related to one another. 



Though the term type is generally employed to desig- 

 nate the great fundamental divisions of the animal 



