654 BIRDS flocks without sound or signal. In some spe- cies which do not sing, there is an amatory call which answers the purpose of song, peculiar to the male bird during the season of the female's incubation, as the clear double whistle of the American quail, the cry of the cuckoo, the cooing of the dove, the harsh craik of the land- rail, and the kek-kek-kek of the male of the English snipe, as it is falsely called in the United States (scolopax Wilsonii), which is either dis- continued, or changed into something different, when the season and the desire for reproducing their species have passed away. As a general rule, aquatic fowl are more noisy than land birds, sea fowl than fresh-water birds, noctur- nal than diurnal birds, domesticated fowls than those in a state of nature, birds which congre- gate than those of solitary habits, and, with the exception of common poultry, migratory birds, which pass much of their time on the wing, than those which dwell on the ground. Nevertheless, while some sea birds which con- gregate are deafening in their clangor, they fly totally independent one of the other, not regu- lating their movements by signals of any kind ; others, as many varieties of the tringa, scolo- pacidce, and charadriada, while they utter no sounds, yet wheel as regularly and orderly, in obedience to some concerted signal, as a well disciplined regiment of horse. And again, while some migratory birds are vociferous in the extreme, others are totally silent, and some non-migratory species, such as jackdaws and rooks, exceed all others in fondness for their own voices. The large proportionate develop- ment of the brain and of the nervous system of birds is another distinguishing feature of their organization. In many cases they exhibit an apparent superiority to the corresponding or- gans in mammalia of the same relative size and weight. Thus, for instance, while in man the size of the brain in proportion to that of the whole body varies from J^ to fa part, that of the common canary bird is -fa. There are, however, great variations in this respect in different families and even in different genera of the same families. Thus, while the brain of the goose is 3-^ of the entire body, that of the eagle is j^-j, and that of the common Euro- pean sparrow is -fa. It differs chiefly from the same organ in mammalia in the presence of certain tubercles corresponding to the corpora striata of other animals, and the absence of several parts found in the brains of the latter. The senses of sight, smell, and hearing are supposed to be most acute in a large propor- tion of the families of the class, much more so than that of taste, which is found well de- veloped in only a few families, and still more than that of touch, which is presumed to be totally wanting. The organs of sight are of great proportionate magnitude, and occupy a large proportion of the cerebral developments. They are constructed with a wonderful con- trivance not inaptly compared with so many peculiar kinds of "self-adjusting telescopes." They are also all provided with a very curious apparatus called the nictitating membrane. This is a fold of the tunica conjunctiva, so ar- ranged as to be capable of being drawn out to cover the eye like a curtain, and to be with- drawn at will, enabling the possessor to meet the brightest rays of the sun undazzled by its brilliance, and protecting the organ from in- juries. With only a few exceptions, birds have no external organs of hearing correspond- ing to an ear. We find instead the aperture called meatus auditorius. The internal mem- branes of this organ are connected with each other by means of the air cells of the skull, and have but a single auditory bone. Among dif- ferent authors there is much diversity of opin- ion in regard to the development of the sense of smell in birds. The experiments of Audu- bon and Bachman would seem to prove that, even in those families in which this sense is presumed to reach its highest point of perfec- tion, the members are directed by sight rather than by smell to their prey. Still it is quite certain that they possess certain nervous de- velopments corresponding to olfactory organs, which, if not designed for smell, possess no very apparent purpose. The sense of taste has a limited degree of development in a few fami- lies, such, for instance, as the divers, the wa- ders in part, and the several families of hum- ming birds, honey-suckers, and a few others. As a general rule it is very imperfect, or even wholly wanting. (For the character of the earliest birds, see AKCH^OPTERYX, and FOSSIL FOOTPRINTS.) The various contrivances and instinctive expedients, by means of which the entire class of aves develop the germs of their mature or perfect ova, are remarkable as well as distinguishing features in the economy of their propagation. They are peculiar to the class, and are without any known exceptions. They are shared with them by no other class of animals, with only occasional but remote approximations, apparent exceptions rather than real. Every individual of the entire class deposits the matured egg without any dis- tinguishable development of the young bird. Lightness and buoyancy of body, whether for flight in the air or for freedom of motion on land or in water, are essential prerequisites in the animal economy of all the various families of the class. So, to nearly the same extent, is also their abundant reproduction. The vast numbers of their enemies, and the many cas- ualties to which they are exposed, render a large and constant propagation necessary for their preservation. It is quite evident that any habit at all corresponding with the gesta- tion of viviparous animals would be inconsis- tent with both of these requirements. It would destroy lightness of body, prevent free- dom of motion, expose to innumerable dangers from enemies, hinder from procuring food, and make fecundity an impossibility. Thus the common quail or partridge (ortyx Virginiana) of the Atlantic states has been known to have
