CATEGORIES OF CLASSIFICATION- 31 



These divisions are, first, the most comprehen- 

 sive groups, the primary divisions, called branches 

 by some, types by others, and divided by some 

 naturalists into so-called sub-types, meaning only 

 a more limited circumscription of the same kind 

 of group ; nest we have classes, and these also 

 have been divided into sub-classes; then orders 

 and sub-orders ; families and sub-families or 

 tribes ; then genera, species, and varieties. With 

 reference to the question whether these groups 

 really exist in Nature, or are merely the expres- 

 sion of individual theories and opinions, it is 

 worth while to study the works of the early natu- 

 ralists, in order to trace the natural process by 

 which scientific classification lias been reached ; 

 for in this, as in other departments of learning, 

 practice has always preceded theory. We do the 

 thing before we understand why we do it: speech 

 precedes grammar, reason precedes logic ; and so 

 a division of animals into groups, upon an in- 

 stinctive perception of their differences, has pre- 

 ceded all our scientific creeds and doctrines. Let 

 us, therefore, proceed to examine the meaning 

 of these names as adopted by naturalists. 



When Cuvier proposed his four primary di- 

 visions of the animal kingdom, he added his 

 argument for their adoption, — because, he said, 

 they are constructed on four different plans. 

 411 the progress in our science since his time 



