70 GENERAL ORNITHOLOGY. 



Zoological Characters. — A "character," iu zoological language, is any point of struc- 

 ture which may be perceived and described for the purpose of comparing or contrasting animals 

 with one another. Thus, conditions of sternum, palate, tarsus, larynx, as noted in preceding- 

 paragraphs, are each of them "characters" which may be used in describing individual 

 birds, or in framing definitions of groups of birds. Morphological characters, with which the 

 classification we have adopted alone concerns itself, may be derived from the structure of a 

 bird considered in any of its relations, or as afi'ected by any of the conditions to which it is 

 subjected. Thus emhryological characters are those afi'orded by the bird during the progress 

 of its development in the egg, from the almost structureless germ to the fully formed chick. 

 Such characters of the embryo in its successive stages are of the utmost significance ; for it is 

 a fact, that the germ of each of the higher organisms goes through a series of developmental 

 changes which, at each succeeding step in the unfolding of its appropriate plan of structure, 

 causes it to resemble the adult state of animals lower than itself in the scale of organization. 

 In fine, the history of the evolution of every individual bird epitomizes tiie history of those 

 changes which birds collectively have undergone in becoming what they are by modified 

 descent from lower organisms. Such transitory stages of any embryo, therefore, give us 

 glimpses of those revolutionary processes which have afi'ected the group to which it belongs. 

 Any bird, for example, when a germ, is at first on the plane of organization of the very lowest 

 known creatures — it is one of tlie Protozoa. As its germ develops, and its structure becomes 

 more complicated by the formation of parts and organs successively difi'erentiated and special- 

 ized, it rises higher and higher in the scale of being. At a certain stage very early reached 

 (for the steps by which it becomes like any invertebrate are very speedily passed over), it 

 resembles a fish in possessing gill-like slits, several aortic arches, no true kidneys, no amnion, 

 etc. Further advanced, losing its gills, gaining kidneys and amnion, etc., it rises to the 

 dignity of a reptile, and at this stage it is more like a reptile than like a bird ; having, for 

 example, a number of separate bones of the wrist and ankle, no feathers, etc. The assump- 

 tion of its own appropriate characters, i. e. , those by which it passes from a reptilian creature 

 to become a bird, is always the last stage. We can thus actually see, inside any egg-shell, 

 exactly those progressive steps of development of the individual bird which we believe to have 

 been taken on a grand scale in nature for the evolution of the class Aves from lower forms of 

 life; and the lesson learned is fraught with significance. It is nothing less than the demon- 

 stration in ontogeny (genesis of the individual) of that plujlogeny (genesis of the phylum) by 

 which groups of creatures come to be. The interior of any adult bird, again, furnishes us with all 

 kinds of ordinary anatomical characters, derived from the way we perceive the diflerent organs 

 and systems of organs to be fashioned in themselves, and arranged with reference to one 

 another. The finishing of the outward parts of a bird gives us the ordinary external characters, 

 in the way in which the skin and its appendages are modified to form the covering of the bill 

 and feet, and to fashion all kinds of feathers. Birds being of opposite sexes, and such difi'er- 

 ence being not only indicated in the essential sexual organs, but usually also in modifications 

 in size or shape of the body or quality of the plumage and other outgrowths, a set of sexual 

 characters are at our service. Birds are also sensibly modified in their outward details of 

 feathering by times of the year when the plumage is changed, and this renders appreciation 

 of seasonal characters possible. All such circumstances, and others that could be mentioned, 

 such as effects of climate, of domestication, etc., in so far as they aff'ect the structure of birds, 

 conspire to produce zoological "characters," as these are above defined. Such characters, 

 according as they result from m(jre or less profound impressions made upon the organism, are 

 of more or less " value" in taxonomy ; being of all grades, from the trivial ones that serve to 

 distinguish the nearest related species or varieties, to the fundamental ones that serve to mark 

 off" primary divisions. Thus the " character " of possessing a backbone is common to all ani- 

 mals of an immense series, called Vertebrata. The " character " of feathers is common to all 



