74 GENERAL ORNITHOLOGY. 
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 Characters.—In a general way, of course, the greater the difference 
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 are 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 fabries the whole 
structure of living beings has been built up. Why is the possession of a back-bone such a 
“fundamental” character 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 thé 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 vertebre so significant? 
Not because all modern birds have saddle-shaped vertebrae, but because to have biconcave ver- 
tebree 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 modern ones, but because teeth 
are a reptilian character. Obviously, to be fish-like 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 Arch@opteryx 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 Lomia leucoptera, and their absence in Loxia curvirostra, 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 rule, 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 
