74 GENERAL ORNITHOLOGY. 



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 oi Loxia leucoptera, and their absence in Loxia ciirvirostra, 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 efi'ective than in remodeling, presumably for the better, the 

 ideas underlying classification. lu 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 possiI>le to decide whether they were of the same or difierent 

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

 them. The same fancy vitiated all ideas upon the subject of genera, families, and higher 

 groups. A "genus" was to be discovered in nature, just like a species; to be named and 

 defined. Then species that answered the definition were "typical;" those that did not do so 

 well were "sub-typical;" those that did worse, were "aberrant." A good deal was said of 

 "types of structure," much as if living creatures were originally run into moulds, like casting 

 type-metal, to receive some indelible stamp ; while — to carry out my simile — it was supposed 

 that by looking at some particular aspect of such an animal, as at the face of a printer's type, 

 it could be determined in what box in the case the creature should be put; the boxes them- 

 selves being supposed to be arranged by Nature in some particular way to make them fit 

 perfectly alongside each other by threes or fives, or in stars and circles, or what not. How 

 much ingenuity was wasted in striving to put together such a Chinese puzzle as these fancies 

 made of Nature's processes and results, I need not say ; suflBce it, that such views have become 

 extinct, by the method of natural selection, and others, apparently better fitted to survive, are 

 now in the struggle for existence. Rightly appreciated, however, the expression which heads 

 this paragraph is a proper one. There are numberless "types of structure." It is perfectly 

 proper to speak of the " vertebrate type," meaning thereby the whole plan of organization of 

 any vertebrate, if we clearly understand that such a type is not an independent or original 

 model conformably with which all back -boned animals were separately created, but that it is 

 one modification of some more general plan of organization, the unfolding of which may or 

 did result in other besides vertebrated animals ; and that the successive modifications of the 

 vertebrate plan resulted in other forms, equally to be regarded as "types," as the reptilian, 

 the avian, the mammalian. Upon this understanding, a group of any grade in the animal 

 kingdom is a "type of structure," of more general or more special significance, presumably 

 according to the longer or shorter time it has been in existence. An individual specimen is 

 "typical" of a species, a species is "typical" of a genus, etc., if it ha.s not had time enough 

 to be modified away from the characters which such species or genus expresses. Any set of 

 individuals, that is, any progeny, which become modified to a degree from their progenitors, 

 introduce a new type; and contiimally increasing modification makes such a type specific, 

 generic, and so on, in succession of time. There must have been a time, for example, when 

 the Avian and Reptilian "types" began to diverge from each other, or, rather, to branch 

 apart from their common ancestry. In the initial step of their divergence, when their respec- 



