34 INTRODUCTION. 



and from this ring the nerves proceed, like rays, to the 

 periphery of the body. The entire body presents a radiant 

 form, for the similar parts are not arranged, as in the Articu- 

 lates, behind one another in rings, but beside one another in 

 a plane. When muscles are present, they are attached to 

 the external, sometimes calcareous, covering of the body. 



Let it not be imagined that this modification is insignificant : 

 and that the invertebrate animals might very properly be opposed 

 to the great .division of vertebrate animals, and be afterwards split 

 up into three* sub-divisions. Such symmetrical separations are 

 usually deceptive, and can only be of real service when the two 

 groups are of equal rank, and are distinguished by positive charac- 

 ters. Beyond doub^t, all natural bodies, for instance, are either 

 Animals or Non-animals: but who, on that account, would think 

 of separating these bodies into an Animal Kingdom, and a Non- 

 animal Kingdom? and the Non-animals again into Plants and 

 Minerals ? Of like value was, in my opinion, the separation of the 

 Animal Kingdom into Vertebrate Animals and Invertebrate Ani- 

 mals : the latter division meaning only " other than vertebrate 

 animals;" it is an indefinite appendage to a defined group, and 

 contains no general idea that can be contrasted with another general 

 idea. 



But what is especially to be attended to in these four great 

 divisions of the animal kingdom is this : that they are not so much 

 distinguished by greater or less perfection of organisation, as by 

 general form, and by the manner in which the parts respectively 

 are related to one another. A great variety of tissues, of organs 

 and of subordinate parts, makes the organisation more complicated 

 or perfect ; but that must be distinguished from the general form, 

 from the plan of the organisation. CuviER did not overlook this 

 truth : and even the name of Fundamental Forms ( Types) , which he 

 is careful to use for these four great divisions, indicates the guiding 

 idea which led him to adopt them. In each type there is a gradual 

 rise and fall of organisation : we descend, says Cuvier, in the type 

 of the Molluscs, from the sepia to the oyster, as in that of the verte- 

 brates, from man to the fish. But it must not be overlooked, that 

 CUVIER did not always sufficiently distinguish the two ideas (the 

 Type and the Perfection of organisation), and to this it is to be 

 ascribed that his division of radiates comprises many animals which 



