2 54 ELEMENTS OE OENITHOLOGT. 



small, it is especially difficult to make this discrimination. 

 Birds, moreover, are creatures which leave behind them com- 

 paratively few fossil remains, while every one now sees that the 

 number of species which have become extinct must be enormous. 

 The best Ornithologists, those even who are the most ardent 

 evolutionists, have come to despair of being ever able to deter^ 

 mine satisfactorily what the exact genetic relations of different 

 groups of Birds really are. We think it then not only the wiser 

 course, but the only course consistent with the interests of the 

 student of science, to abstain from making any positive asser- 

 tions as to the genetic affinities of different Bird-groups. On 

 the other hand, we do not by any means deny the truth of the 

 theory which would ascribe real blood-relationship to different 

 groups of Birds. We desire to keep an open mind with respect 

 to questions of this kind, and we would advise our readers to do 

 the same. In the meantime we wish to avail ourselves of the 

 most recent labours of Ornithologists in this cause, and to give 

 the greatest weight to characters which may fairly be supposed 

 to indicate real relationship by descent. Characters of the 

 kind would have been regarded as essential and fundamental 

 ones even before the theory of evolution became popular — 

 we mean characters derived from the form of the skeleton and 

 other anatomical peculiarities and from the mode of the process 

 of the development of the young. 



We may thus legitimately speak of "real affinity,'' "true 

 relationship," and " essential connection," as existing between 

 certain Birds, whether or not a real genetic affinity exists 

 between them. If such genetic affinity does exist between 

 such Birds, then such a mode of speech has a plain and obvious 

 truth and fitness. But if such genetic affinity does not exist 

 between them, then such expressions must be understood to 

 denote resemblances such as were recognized as being of a 

 " deeper" kind than some other resemblances, before questions 

 of descent had begun to be discussed. A " deep resemblance " 

 of this kind is one which is the sign of a great many other 

 resemblances, whereas a " superficial resemblance " has no such 

 significance. 



This great uncertainty as to the full significance of characters 

 which no one can call " superficial," causes the classification of 

 Birds to be a more or less arbitrary one. The arbitrary nature 

 of Ornithological grouping is intensified by the habit which has 

 so long and widely prevailed of not even attempting to define the 

 groups by any constant and universal anatomical characters. 



