Birds. 105 



Putting this statement in diagrammatic form, with respect 

 to North American Birds only, would give us the following 

 in ascending series from the largest group to the smallest, — pre- 

 mising that eacli group includes all those beyond it, and sprouting 

 from it. See Fig. 3. 



We have then as the chief groups into which living things are 

 classified 



Kingdoms — based on materials of structure. 



Sub-kingdoms, based on plan of structure. 



Classes, " " larger details of deep structure. 



Orders, " " smaller details of deep structure. 



Families, " " smallest details of deep structure. 



Genera, " " larger details of external structure. 



Species, " " smaller details of external structure. 



To these there are added, 



Varieties — based on the smallest details of external structure. 

 Where varieties are apparently constant in their differences from 

 '(he main species and such constancy can be attributed to peculiar 

 conditions of environment, the term "variety" gives way, in mod- 

 ern advanced terminology to "sub-species" or "incipient" species, 

 the inference being that a new species is in process of development. 



While all these' groups then are arbitrary in one sense, they 

 are the result of a general agreement of biologists as to what 

 constitutes importance in variation and relationship in structure. 



The aim of Zoological classification as already stated, is to 

 indicate relationship. 



Now, the question maybe asked by some "of what use is this 

 (apparently) complicated system of classification ? " 



We may reply : 



First : it satisfies the mind in its desire to study the relationship 

 of all living things. 



Secondly : it conduces to economy of time and labor in (a) 

 the recording of facts, (b) the identification of specimens, and (<"), 

 the reference to literature. 



In order to illustrate one of these uses of classification : sup. 

 pose a person with no knoweledge whatever of birds was to come 

 into possession of a common North American Robin, and desired 

 to read something of its history and habits. First, of course, he 

 must know its name, in order to find it in the books. 



Now supposing the most accurate description of all our North 



