Page:Bird-lore Vol 01.djvu/369

The Orientation of Birds BY CAPTAIN QABRIEL REYNAUD. French Army Translated t'rtmi the French by Mrs. Clara J. Coxe (Concluded from page loS) E have demonstrated that the combined working of the five ■^ senses is limited, and is not sufficient to explain the act of distant orientation. The latter is governed by a par- ticular organ that we have called the sense of direction. This sense has its seat in the semi-circular tubes of the ear. Numer- ous experiments have proved that an}' lesion which impairs this organ brings an immediate disturbance in the faculty of orientation of the injured bird. The semicircular tubes of vertebrated animals are made up of three little anserated membranes filled with a liquid called endolympii. These three semicircular conformations are independent of each other, except in a point where their cavity is common, or where they issue in a little sack called utriculc. They are generally situated in three perpendicular planes. Next to the wonderful experiments of Flourens in 1824, and the autopsies of Menieres, their operation has been studied by Czermak, Harless, Brown-Sequard, Vulpian Boetticher, Goltz, Cyan, Brewer, Mach, Exuer Bazinski, Munck, Steiner, Ewald, Kreidl, Pierre Bonnier. We know now that their function is directl}' in harmony with the exer- cise of equilibration and quite independent of the sense of hearing. jIr. P. Bonnier, after studying in all the animal series the character of the organs which precede the labyrinthic formations, and lastly these themselves, in combining the records of comparative anatomy and physiology, and verifying them by clinical surgery, has been able to demonstrate that these organs lead directly to what he calls the sense of altitudes, which supplies the figures or images of position, of distribution and, consequently, movement and displacement in space. We do not yet know in any very precise : way the physiological excitant which governs the semicircular canals. While w^aiting until new researches permit us to settle this interesting point, we will try to determine the method of the operation of the sense of direction. This way of proceeding has nothing, after all, illogical in it. In the natural sciences, as well as in others, the knowledge of effect pre- cedes that of cause. The animal entering upon unknown ground takes on his return the reverse scent of the road, more or less sinuous, followed in going ; arriving in known ground he directs himself to reach his end in a straight line. The Carrier Pigeon freed at 500 kilometers from his cote, on his {141)