BIRD. 



303 



organs as the system of nourishment, the wings as the 

 organs of motion in the air, and the feet as organs of 

 motion, we iiml that not even any two of them vary 

 according to the same law, so that we cannot form a 

 classification, even upon the relations which they bear 

 to each other. 



Thus, while birds are remarkably well defined as a 

 class, while they are among the most interesting 

 of all nature's productions, and while in their indi- 

 vidual habits in wild nature, they are more acces- 

 sible to our observation than, perhaps, any other 

 animals, they are perfect puzzles when we attempt to 

 systematise them ; and almost the best that we can 

 do is to go to wild nature, and study them individually 

 in forest, field, or flood. 



Their double motion, that of the feet and that of 

 the wings, which is so modified that it becomes the 

 four motions of walking, Hying, swimming, and div- 

 ing, is the chief cause of the perplexity. Some birds, 

 as the common swift, have very little motion, save the 

 aerial one ; others, such as the ostrich, have none 

 but the terrestrial one : some again, as the penguins, 

 have very little more than the aquatic ones ; and 

 some, such as the pochard ducks, luve all the four. 

 Those which have the same kinds of motions have the 

 one or the other predominating in an endless variety of 

 degrees ; and the character of the bill, according to the 

 motions which we observe from other species, some- 

 times agrees more with the one system of nature, and 

 sometimes with the other. All these perplexing cir- 

 cumstances increase the interest of the study of 

 birds, at the same time that they increase the diffi- 

 culty , and therefore, though none of the systems are 

 quite consistent that is, though no single character 

 can be carried through the class there has been no 

 want of systems, or of ability in the formation of 

 them. We have no desire to add another to the 

 number, as the labour would be but of little value, 

 and in this work out of place; so we shall chiefly fol- 

 low that of Cuvicr, though with some slight varia- 

 tions. The necessity which Cuvier, who had studied 

 the structure of animals intimately, and endeavoured 

 to arrange them according to it, found himself under 

 of sometimes using the bills, sometimes the feet, and 

 s nnetimes the wings, as the leading characters of his 

 subdivisions, shows very forcibly the difficulty which 

 attends this class of animals. 



But before any system can be made intelligible to 

 those who do not already understand the subject, we 

 must give some explanation of the structures and 

 functions on which the systematic arrangement is 

 founded ; and this will be rendered more easy of 

 consultation by marking- it off into portions under 

 separate titles. 



I. GENERAL CHARACTERS oi 1 THE CLASS. Birds 

 consist of a head, neck, trunk, tail, and four limbs or 

 extremities. The head is in general small in pro- 

 portion to the whole animal ; and the jaws are pro- 

 duced and terminate in horny mandibles, which open 

 and shut horizontally, forming the bill, which, except- 

 ing in those species which kill prey, is the chief or the 

 sole instrument in feeding. The bill varies much, 

 both in the form and in the consistency of the man- 

 dibles. In some it serves as a pair of strong pincers 

 for tearing flesh; in others it is a spear for transfixing ; 

 in others again ir, is adapted for hewing into timber ; 

 or it is fitted for boring into the ground or for dabbling 

 in the sludge at the bottom of shallow waters, in which 

 cases it is understood to have a sentient covering, so 



that it can both find and seize the food. Sometimes 

 it is borne open as the bird Hies, ami catches insects 

 as in a net ; in other cases it catches by snapping. 

 In some it is fitted for breaking the hard shells of 

 fruits ; in others for cleaving pulpy ones, or raising 

 the scales of cones so as to get at the seeds. The 

 modes of using it arc; indeed exceedingly varied ; for 

 birds are almost universal feeders, both in regard of 

 substance and of situation ; and wherever a bird's 

 food is to be found, there is generally a bird to eat it, 

 and the bill of that bird is always very well adapted 

 for taking it. But the office of the bill ends with the 

 prehension of the food, or the dividing of it into such 

 portions as can pass the gullet (which is generally 

 capable of considerable distension) into the stomach; 

 and there is no mastication, or chewing by the mouth, 

 of birds, and no apparatus for the performing of such 

 an office. 



The organs of smell, sight, and hearing, are placed 

 in the head ; the nostrils at the base of the bill, in 

 the substance of it, or even near its extremity, accord- 

 ing to the habit ; and they are variously defended by 

 feathers, hairs, scales, and valvular membranes. 



The eyes of birds are placed in the sides of the 

 head, generally speaking better adapted for seeing 

 under them or laterally than above them or directly 

 in front. But the position varies with the habit : birds 

 which prey only in clear light and under them have 

 the eyes far apart, and shaded ; while those which 

 prey in the twilight have them turned more to the 

 front. The eye is better fortified than in the mam- 

 malia ; the anterior part of the ball has a circle of 

 bone ; and there is a nictitating membrane, or third 

 eyelid, which, when not used, is protected from the 

 action of the weather by a lodgment in the inner 

 canthus of the eye. It is thus more soft and moist 

 than an exposed eyelid, and it works over the whole 

 eye in a direction crosswise to the usual opening. 

 The corner of the eye is very convex, and beauti- 

 fully clear ; but the crystalline lens is rather flat. 

 The eyes of birds are in many instances much more 

 exposed to the action of the weather than the eyes of 

 most other vertebrated animals, and they appear to be 

 the organs of sense upon which birds have their chief 

 dependence ; and, true to the general law of nature, 

 that the supply is always proportionate to the want, 

 they are furnished and fortified in an extraordinary 

 manner. 



The ears of birds, within the bones of the head, are 

 well formed ; but, with the exception of nocturnal 

 feeders, which are, of course, much guided by the 

 ear, they have little or no external concha. The 

 nocturnal ones (the owls especially) have external 

 ears ; but the openings of the ears of all birds are 

 concealed by feathers, generally of a more downy 

 character than those on the neighbouring parts. 

 These protect the ear from the violent action of the 

 air when the bird is in rapid flight, and also preserve 

 a uniform temperature in that delicate organ. 



The neck of birds does not, like that of the mam- 

 malia, consist of the same number of vertebne iti all 

 the species, but varies much according to tlio habit of 

 the bird. In some it is verv long, and in others 

 moderate, but in all it is susceptible of much motion, 

 and of motion in all directions ; so that generally 

 speaking, the point of the bill commands the whole 

 space within reach of the extended neck, and also all 

 parts of the body of the bird. The vertebrae are also 

 articulated in such a manner as that the greatest and 



