74 GENEBAL ORNITHOLOGY. 



be a difference of "family"? What shall he "generic" and what "specific" differences'? 

 Such questions are more easily asked than answered. They demand critical consideration. 



Valuation of Characters. — In a general way, of course, the greater the diflerence 

 between any two objects, the more "important" 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 arp classifying morphologically, 

 and upon the theory of Evolution ; and in such a system a character is important or the 

 reverse, simply as an exponent of the principles, or an illustration of the facts, of evolutionary 

 processes of Nature, according to the unfolding of whose plans of animal fabrics the whole 

 structure of Uving beings has been built up. Why is the possession of a back-bone such a 

 "fundamental" charact«r that it is used to establish one of the primary branches of the animal 

 kingdom? It is not because so many millions of creatures possess it, but because it was 

 introduced so early in the evolutionary process, and because its introduction led to the most 

 profound modification of the whole structure of the animals which became possessed of a 

 vertebral column. Why is the possession by a bird of biconcave vertebrre so significant ? 

 Not because all modem birds have saddle-shaped vertebrse, but because to have biconcave ver- 

 tebrae is to be quoad hoc fish -like. Why is presence or absence of teeth so important? Not that 

 teeth served those old birds better than a horny beak serves modem ones, but because teeth 

 are a reptilian character. Obviously, to be fish-Mke or reptile-like is to be by so much unbird- 

 like ; the degree of difference thus indicated is enormous ; and a character that indicates such 

 degree of difference is proportionally " important " or " fundamental," — just what we were 

 after. By knowledge of facts like these, and by the same process of reasoning, a naturalist of 

 tact, sagacity, and experience is able to put a pretty fair valuation upon any given character ; 

 he acquires the faculty of perceiving its significance, and according to what it signifies does it 

 possess for him its taxonomic importance. As a matter of fact, it seems that characters of all 

 sorts are to be estimated chronologically. For, if animals have come to be what they are by 

 any process that took time to be accomplished, the characters earliest established are likely to 

 be the most fundamental ones, upon the introduction of which the most important train of 

 consequences ensue. Feathers, for example, as the Archmopteryx teaches us, were in full 

 bloom in the Jurassic period, and they are still the most characteristic possession of birds : 

 all birds have them ; they are a class character. If they had been taken on quite recently, we 

 may infer that many creatures otherwise entirely avian might not possess them, and they 

 would have in classification less significance than that now rightly attributed to them. On 

 the other hand, we cannot suppose that the finishing touches, by which, in the presence of 

 white bands on the wings of Loxia leitcoptera, and their absence in Loxia eurvirostra, these two 

 " species " are distinguished, were not very lately given to these birds. It is a very late step 

 in the process, and correspondingly insignificant ; it is of that value or importance which we 

 call " specific." The same method of reasoning is available for determining the value of any 

 character whatever, and so of estimating the grade of the group which we establish upon such 

 character. As a mle, therefore, the length of time a character has been in existence, and its 

 taxonomic value, are correlated, and each is the exponent of the other. 



"Types of Structure." — In no department of natural history has the late revolution in 

 biological thought been more effective than in remodelling, presumably for the better, the 

 ideas underlying classification. In earlier days, when "species" were supposed to be inde- 

 pendent creations, it was natural and almost inevitable to regard them as fixed facts in nature. 

 A species was as actual and tangible as an individual, and the notion was, that, given any two 

 specimens, it should be perfectly possible to decide whether they were of the same or different 

 species, according to whether or not they answered the " specific characters " laid down for 



