CLASSIFICATION. 



The first step in any science is that of classification. The present 

 system of generic grouping of species was first advanced by Linnseus in 

 his epoch-making "Systema Naturae" and has since been followed con- 

 sistently by zoologists. By this, species are grouped together in genera 

 according to fundamental structural relationships and not accidental 

 resemblances. The fact that upon the discovery of the laws of evolution 

 these relationships were found to agree with lines of descent proved the 

 logic of the system and gave it an added meaning. Thus the various 

 specific members of a genus can be conceived as having descended from a 

 common specific ancestor; the genera of a family from a common generic 

 one, etc. 



Dealing only with existing North American birds, they may be divided 

 into a number of Orders, which are the largest groups with which the 

 Canadian ornithologist has direct concern. Orders are divided into 

 Families, Families into Genera, and Genera into Species. These divisions 

 may be again subdivided into Suborders, Subfamilies, Subgenera, and 

 Subspecies whose positions in the scheme are evident from their titles. 



Though the limitations of book construction necessitate the presenta- 

 tion of the classification scheme as a linear succession of forms following 

 one another in single file, it should be borne in mind that the system is 

 not linear in conception. The component species instead of following a 

 single line of relationship and sequence from the lowest to the highest 

 present many parallel or divergent lines of equal or subordinate rank. 

 The class Aves or Birds may be represented by a tree, the height of the 

 tree representing time in geological ages from the earliest at the bottom 

 to the present near the top. The trunk should be shown as double at the 

 base; one stem would be a short dead stump and would represent the 

 fossil, toothed birds which became extinct before present geological time; 

 the other, large and thrifty, would represent the modern untoothed forms. 

 This in turn would divide into two main branches a short way from the 

 base and would represent the two subclasses, the Raft-breasted and the 

 Keel-breasted birds. The former would be represented by much the 

 smaller branch, whereas the latter would divide and subdivide into 

 branches representing first, orders; next, families; then, genera; and 

 finally, species. 



The value of these divisions, that is, the amount of differentiation 

 sufficient to raise a group of genera to a family, or a collection of families 

 to an order, is a matter for experienced individual decision as there is no 

 authoritative ruling upon the subject. However, there has gradually 

 grown up an approximate agreement on this subject, though the constant 

 tendency among specialists has been to make finer and finer distinctions 

 and to multiply the number of the various groups. 



The smallest division generally accepted is the Species. Though 

 everyone has a more or less accurate conception as to what a species is, 

 whether it be called by that name or another, no satisfactory definition 

 has ever been constructed for it. It is what is commonly known as a 

 "kind of an animal." Thus the horse is a different "kind" or species 

 from a donkey, a bluebird from a robin. They are sharply marked off from 



