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 ; next 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 has 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. 

 All the progress in our science since his time 



