The Orientation of Birds 



BY CAPTAIN GABRIEL REYNAUD. French Army 



'I'raiislatrd liom the ImimkIi by Mrs. Clara J. Cnxc 



( Concluded from page lob) 



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 any 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 endolympli. 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 iiiricule. 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 directly in harmony with the exer- 

 cise of equilibration and quite independent of the sense of hearing. 

 Mr. 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 waiting 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) 



