THE LAWS OF ORIENTATION AMONG ANIMALS. 491 



a journey, is for any reason not present at the departure of bis com- 

 panions, he does not go away. This is why woodeocks, 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 cap- 

 tivity 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 knowl- 

 edge 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 suffi- 

 cient 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 fol- 

 lowed 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. 



y. 



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 Meniere, their working was studied by Czermak, Harless, 

 Brown-Sequard, Vulpian,Boetticher,Goltz,Cyon, Crum-Brown, Brewer, 

 Mach, Exner, Bazinsky, Munck, Steiuer, Ewald, Kreidl, and Pierre 



