2^6 AVERS. [Vol. VI . 



more especially nearest kin — in case it or they were in any way 

 hindered from performing the proper function to its full or even 

 a sufficient extent, — e.g. as when the sensory hairs are loaded 

 down with otoliths. Indeed, so far as the auditory function is 

 concerned, one sense organ might be made to serve all the audi- 

 tory needs of the animal ; and, had not the inherited tendency 

 to divide compelled the primitive vertebrate ear to progress by 

 the further division of its auditory sense organs, in all probabil- 

 ity no such canal complex as exists in most forms would ever 

 have been produced ; but the enlarging physiological necessities 

 might have been met by the differentiation of the original estab- 

 lishment, after much the same plan we find followed by the 

 mammalian cochlear organ in its development, or of the retina 

 in the eye. As an instance of the moulding influence which the 

 view heretofore held of the relation of the two prime chambers 

 of the ear to each other, exercised not alone on morphological 

 ideas, but physiological as well, I may cite Paul Meyer's state- 

 ments, made in harmony with the earlier ones of Hasse, that 

 the accepted division of the auditory vesicle into superior and 

 inferior parts was no less important for physiology than for 

 anatomy. The superior part had, by entering into more inti- 

 mate relations with the bony walls of the cranium and the reduc- 

 tion of its perilymphatic spaces, acquired the (or restricted its) 

 function to the perception of vibrations transmitted through the 

 bone, while the inferior part, by entering into intimate relation 

 with the tympanic transmission apparatus, and by the enlarg- 

 ment of its perilymphatic spaces, has acquired the (or enlarged 

 its) function to the perception of vibrations coming through 

 the tympanic apparatus. This differentiation has become the 

 more perfect by the almost complete separation of the two parts 

 from one another. 



Such are Hasse's and Meyer's views ; but I have shown that 

 in vertebrates as low as the Elasmobranchs, the utriculus and 

 sacculus are nearly as completely isolated as in mammals, and 

 furthermore, after the general consideration of the relation of 

 canal organs to the surface of the body (their relation to the 

 close investment by membrane bones, as in fishes, included), it 

 does not seem to be a specially pregnant idea that the sense 

 organs of the semicircular canals and the utriculus are only 

 capable of, or are restricted to, the perception of vibrations 



