144 ESSAY ON CLASSIFICATION. Part I. 



character, as to designate the primary divisions of the animal kingdom. We 

 speak, for instance, of specific types, generic types, family types, ordinal types, 

 classic types, and also of a typical structure. The use of the word type in this 

 sense is so frequent on almost every page of our systematic works, in Zoology 

 and in treatises of Comparative Anatomy, that it seems to me desirable, in order 

 to avoid every possible equivocation in the designation of the most important great 

 primary divisions among animals, to call them branches of the animal kingdom, 

 rather than types. 



That, however, our systems are more true to nature than they ai'e often sup- 

 posed to be, seems to me to be proved by the gradual approximation of scientific 

 men to each other, in their results, and in the forms by which they express those 

 results. The idea which lies at the foundation of the great primary divisions 

 of the animal kingdom is the most general concejotion possible in connection with 

 the plan of a definite creation; these divisions are, therefore, the most comprehensive 

 of all, and properly talce the lead in a natural classification, as representing the 

 first and broadest relations of the difl'erent natural groups of the animal kingdom, 

 the general formula wliich they each obey. What we call branches expresses, in 

 fact, a purely ideal connection between animals, the intellectual conception which 

 unites them in the creative thought. It seems to me that the more we examine 

 the true significance of this kind of groups, the more we shall be convinced that 

 they are not founded upon material relations. The lesser divisions which succeed 

 next are founded upon special qualifications of the plan, and differ one from the 

 other by the character of these qualifications. Should it be found that the features 

 in the animal kingdom which, next to the plan of structure, extend over the largest 

 divisions, are those which determine their rank or respective standing, it would 

 appear natural to consider the orders as the second most important category in the 

 organization of animals. Experience, however, shows that this is not the case ; 

 that the manner in which the plan of structure is executed leads to the distinction 

 of more extensive divisions (the classes) than those which are based upon the com- 

 plication of structure (the orders). As a classification can be natural only as far as 

 it expresses real relations observed in nature, it follows, therefore, that classes take 

 the second position in a system, immediately under the branches. We shall see 

 below that orders follow next, as they constitute naturally groups that are more 

 comprehensive than families, and that we are not at liberty to invert their respec- 

 tive position, nor to transfer the name of one of these divisions to the other, at 

 our own pleasure, as so many naturalists are constantly doing. 



