112 GENERAL ORNITHOLOGY part n 



conventionally designated as those of da&s, order, family, genus, and 

 species; always accepted in the order here given, from higher to 

 lower groups. (There are various others, and especially a number 

 of intermediate groups, generally distinguished by the prefix sub-, as 

 sub-family ; but those here given are generally adopted by English- 

 speaking naturalists, and suffice to illustrate the point I wish to 

 make.) It may sound like a truism to say that groups of the same 

 grade, bearing the same name, whatever that may be, must be of 

 the same value, — must be based upon and distinguished by charac- 

 ters of equal or equivalent importance. Equivalence of groups is 

 necessary to the stability and harmony of any classificatory system. 

 It will not do to frame an order upon one set of characters here, 

 and there a family upon a similar set of characters ; but order must 

 differ from order, and family from family, by an equal or corre- 

 sponding amount of difference. Let a group called a family differ as 

 much from the other families in its own order as it does from some 

 other order, and by this very circumstance it is not a family but an 

 order itself. It seems a very simple proposition, but it is too often 

 ignored, and always with practical ill result. Two points should be 

 remembered here : First, that absolute size or numerical bulk of a 

 group has nothing to do with its taxonomic value : one order may 

 contain a thousand species, and another be represented by a single 

 species, without having its ordinal valuation affected thereby. 

 Secondly, any given character may assume different importance, or 

 be of different value, in its application to different groups. Thus, 

 the number of primaries, whether nine or ten, is a family charac- 

 ter almost throughout Oscines; but in one oscine family {Vireonidm) 

 it has scarcely generic value. It is difficult, however, to determine 

 such a point as this without long experience. Nor is it possible, in 

 fact, to make our groups correspond in value with entire exactitude. 

 The most we can hope for is a reasonable approximation. As in the 

 thermometric simile above given, " blood-heat " and other points 

 fluctuate, so does order not always correspond with order, nor 

 family with family, in actual significance. What degree of differ- 

 ence shall be "ordinal" ? "What shall be a difference of "family"? 

 What shall be " generic " and what " specific " differences ? Such 

 questions are more easily asked than answered. They demand 

 critical consideration. 



Valuation of Charaeters. — In a general way, of course, the 

 greater the difference between any two objects, the more " import-^ 

 ant" or "fundamental" are the "characters" by which they are 

 distinguished. But what makes a character "important" or the 

 reverse ? Obviously, what it signifies represents its importance. 

 We are classifying morphologically, and upon the theory of Evolu^ 

 tion ; and in such a system a character is important or the reverse, 



