144 THE MEMBRANOUS LABYRINTH OP CERTAIN ANIMALS. [Mar. 7, 



of the bird, it has to be recorded that these animals have otoHths 

 considerably larger than those of mammals with the exception 

 of the Seal as noted before. They are two in number and are 

 almost in contact. One is a flat plate, and lies in the vipper and 

 posterior portion of the vestibule ; the second is round and appears 

 to lie on the first. 



Without going into the physiology of the vestibule and canals 

 as ascertained by laboratory experiments, I would like to make a 

 few remarks on the bearing which these structures may have upon 

 the migrations of animals. 



We know, from clinical' and experimental evidence, that the 

 semicircular canals furnish the individual with an accurate know- 

 ledge of the extent to which the head has been rotated in space, 

 whether this has been carried out by a voluntary effoi't on the 

 part of the individual or by some external agency. Now, bearing 

 this fact in mind, it has long since occurred to me that by this 

 means we may, in part, be able to account for that mystery which 

 has long puzzled the naturalist : the faculty by wliich many 

 animals pursue their long migrations. Almost all birds migrate, 

 a great many fishes, and even some mammals such as the Seal. 

 That they cannot guide themselves by the sense of sight entirely 

 is obvious, since they may pvirsue their flight undeterred by the 

 darkest night and through blinding fog. Furthermore, it is . 

 difficult to understand how fishes and seals can obtain much 

 information by vision ; and, indeed, it is clear that some other 

 sense must be employed, though vision may undoubtedly help. 

 The same diificulty occurs in the case of the Corn-Crake, which 

 appears to do its migration on foot, and vision can hardly avail it 

 very much on its journey. 



But the sense of direction may be obtained by other means than 

 by the eye, namely by the semicii-cular canals and the vestibule. 

 When a particular canal of one side is injured, the animal tends 

 to rotate in a particular direction, thus indicating that the canal 

 in question regulates the movements of the animal in that 

 direction. 



Of course this explanation does not account for the orienting 

 process which the bird must go tlirough before it starts its flight, 

 but only for the faculty it possesses of pursuing the course 

 correctly through the night or fog without having recourse to the 

 sense of sight. How the orienting process is carried out, I do 

 not pretend to explain, though it may be done perhaps by 

 observing the position of the setting sun or by the bearing of 

 surrounding objects. 



Few mammals migrate in the proper sense of the term, and even 

 those which do appear to do so, go from place to place in quest of 

 food. The Seal, however, is one example of a mammal which does 

 migrate in the strict meaning of the word, returning to a circum- 

 scribed breeding-place every year in a manner similar to the bird 

 and the fish. 



Now it is rather remarkable, that of all mammals the vestibule 



