PREFACE. V 



species of Plovers, Sandpipers, and Snipes. The first difficulty to be overcome was the 

 determination of the species. 



Most English ornithologists regard species as fixed quantities to be accepted or 

 rejected according to circumstances. The hereditary conservatism of Englishmen has for 

 the most part prevented them from realizing the important fact, that if the theory of 

 evolution be true there must always be species in process of being evolved or differ- 

 entiated. They have accepted the theory of evolution without accepting its inevitable 

 consequences. 



The hereditary progressive tendency of American thought has prevented the ornitho- 

 logists of that country from committing the same blunder, and with them the recognition 

 of subspecies is as much a matter of course as the admission that many species, even 

 amongst those whose range of geographical distribution is very wide, shov,- no tendency to 

 split up into local races. 



In this case no reasonable man can doubt that the Americans are perfectly right, and 

 the majority of Englishmen hopelessly wrong. 



The imperative necessity of recognizing subspecies immediately started the difficulty 

 of their definition. To define the indefinite is no easy task, but the imperfection of the 

 systems of nomenclature makes it absolutely necessary. I flatter myself that I have hit 

 the happy medium by defining the difference between two forms to be specific in all cases 

 where they do not intergrade, without making unnecessary inquiries as to the reasons why 

 they do not do so ; and to be only subspecific in all cases where they do interyrade, without 

 making unnecessary inquiries as to how the intergradation is accomplished. 



Having thus satisfactorily settled one boundary of subspecies, I decided to define the 

 other boundary geographically. Whatever individual variation be found within the range 

 of a species, if it be not also capable of being defined geographically I do not regard it of 

 subspecific value. 



My next difficulty was the definition and limitation of genera. The prse-Darwinian 

 ornithologists supposed that species differed in colour, and genera in what they were 

 pleased to call structural characters, such as the shape of the bill, feet, wings, tail, &c. 

 Here it seems to me that both English and American ornithologists are for the most part 

 wrong. 



The post-Darwinian ornithologist must approach the subject from an entirely different 

 standpoint. No a priori theories as to the respective generic value of colour and structure 

 can be tolerated for a moment. It may be a matter of opinion as to how far a genus should 

 be permitted to extend, but it is an inexorable law that no species can be admitted into a 

 genus unless it be nearer related to some one species in that genus than it is to any or 

 every species outside. Modern genera mast be genetic, they must indicate affinity ; but 

 genera founded upon the shape of the bill or the number of the toes often associate birds 

 too-ether whose similarity is only one of analogy, where Hke causes have produced like 



