22 INTRODUCTION. 



Clamcitores or non-singers ;^^ likewise the Turdidce consists of 

 the Txirdince, or typical thrushes, who have a "booted" tarsus, 

 and the Miminm^ or mocking-thrushes, who do not possess this 

 feature. Combinations of less important distinctions in struct- 

 ural detail characterize the genera; and therefore birds be- 

 longing to the same genus have exactlj"- the same structure. 

 The difference between sjjecies is marked by coloration, and 

 often size. To illustrate the foregoing, take as a subject the 

 common Song Sparrow. He belongs to the Insessorian group, 

 the order of Passeres, and the suboixler Oscines. His family 

 is that of the FringillidcB^ or finches, and his genus Melospiza. 

 His specific name is melodia, but there is also a variety, M. 

 fallax. " Extremely similar ; wings and tails slightly longer ; 

 paler, grayer ; the streaks not so obviously blackish in the 

 centre. "Whole of the Rocky Mountains and Great Basin ; 

 scarcely distinguishable." (Coues.) 



§ W. The classification of birds (or other objects in nature) 

 necessarily entails certain absurdities, being more or less artifi- 

 cial. The method of modern classification is that of descend- 

 ing from the higher to the lower groups, but sequence is too 

 often insisted on among groups, which diverge (so to speak) 

 from a common centre. The division of families, genera, etc., 

 is more or less arbitrary, a certain degree of difference being 

 necessary to separate them, whereas minor (or fractional) 

 differences cause intermediate groups. Let X I'epresent tlie 

 degree of dissimilarity between two genera; then ^ represents 

 the difference between two subgenera (of the same genus) ; 

 1 -|- -^ between subfamilies, 2 X between families, 2-{- - be- 



><* A rather technical distiuction. 



