a journey, is for any reason not present at the departure of his companions, he does not go away. This is why woodcocks, wounded, and consequently unfit to undertake a long journey, resign themselves to remaining in our country another year. The same thing has been noticed of plovers, of curlews, of storks, and of swallows held in captivity at the time of the departure of their companions. Some of these birds endure the inclemencies of the winter climate; others, especially the swallows, succumb to them.
Thus, then, it is by means of a sort of tradition that the migratory birds transmit to each other from generation to generation the knowledge of the airy paths they follow. These paths once laid out are unchangeable.
The path of the quail that come to Provence from Africa, or of the woodcocks that alight in Jersey, is well known to the peasants, who capture them by thousands. To baffle their enemies it would be sufficient for the poor birds to change their path only a few kilometers. But they can not do it; they are fatally bound to this aerial route followed in their last journey, and they can not deviate from it or they will be lost.
Like other animals, fish also are districted; certain of them have, like migratory birds, two or three dominions which they successively occupy. To go from one to the other they emigrate en masse, following routes subject to the same rules as those we have explained for the migration of birds. The desperate war waged against them by fishers who know their habits has never decided them to change their route.
Our theory of orientation seems therefore applicable to animals of every species; it enables us to arrange properly and satisfactorily a number of facts observed and known for some time.
V.
We have demonstrated that the combined play of the five senses, whose range is limited, is not sufficient to explain orientation from a distance. This faculty is governed by a distinct organ, which we have called the sense of direction. The sense has its seat in the semicircular canals of the ear. Numerous experiments have, in fact, proved that any lesion which injures this organ results in immediate impairment of the faculty of orientation in the patient.
The semicircular canals of vertebrates are formed of three little membranous passages filled with a fluid called endolymph. They are independent of one another except at one point, where they have a common cavity, and open into a little sac called the utricle. They are situated, generally speaking, in three mutually perpendicular planes.
After the remarkable experiments of Flourens in 1834 and the autopsies of Ménière, their working was studied by Czermak, Harless, Brown-Séquard, Vulpian, Boetticher, Goltz, Cyon, Crum-Brown, Brewer, Mach, Exner, Bazinsky, Munck, Steiner, Ewald, Kreidl, and Pierre
