CLASSIFICATION. 7 
are shed, and fresh ones take their place, either over a part or the whole of 
the body. The change frequently or generally results in considerable differ- 
ences of color, constituting the “seasonal plumages” of so many birds, 
which, in the same bird, may change from black to white even, from plain 
to variegated, from dull to brilliant. But birds also change colors, by actual 
alteration in the tints of the feathers themselves, and by gaining new ones 
- without losing any old ones. The generalization may be made, that when 
the sexes are strikingly different in color, the young at first resemble the 
female; but when the old birds are alike, the young are different from 
either. When the seasonal changes are great, the young resemble the fall 
plumage of the old. When the old birds of two different species of the 
same genus are strikingly alike, the young of both are usually intermediate 
between them, and different from either. 
Besides being the most highly developed, most complex, wonderfully per- 
fect and beautiful kind of tegumentary outgrowth; besides fulfilling the 
obvious design of covering and protecting the body, the plumage has its 
§ 11. Psounrar Orrice: that of accomplishing the act of flying. For 
all vertebrates, except birds, that progress through the air—the flying-fish 
with its enlarged -pectoral fins; the flying reptile (Draco volans) with its 
skinny parachute ; the flying mammal (bat) with its great webbed fingers — 
accomplish aérial locomotion by means of tegumentary expansions. Birds, 
alone, fly with tegumentary outgrowths, or appendages. 
SECT. II. An aLtusion TO THE CLASSIFICATION OF Brrps— TAXxon- 
omy — STRUCTURE — CHARACTERS — Groups OF DIFFERENT GRADES— 
Types AND ABERRATIONS— EQUIVALENCY— ANALOGY AND AFFINITY 
— EXAMPLE. 
Serine what a bird is, and how distinguished from other animals, our 
next business is to find out how birds are distinguished from each other ; 
when we shall have the material for 
§ 12. CrassrricaTion, a prime object of ornithology, without which, 
birds, however pleasing they are to the senses, do not satisfy the mind, 
which always strives to make orderly disposition of things, and so discover 
their mutual relations and dependencies. Classification presupposes that 
there are such relations, as results of the operation of fixed inevitable law ; 
it is, therefore, 
§ 13. Taxonomy (Gr. fais, arrangement, and nomos, law), or the ra- 
tional, lawful disposition of observed facts. Just as taxidermy is the art 
of fixing a bird’s skin in a natural manner, so taxonomy is the science of 
arranging birds themselves in a natural manner, according to the rules that, 
to the best of our knowledge and belief, are deducible from examination of 
their 
‘ § 14. Srrucrure: The physical constitution of a bird ; all the material 
constituents of a bird, and the way its parts or organs are put together. 
