2 So AVERS. [Vol. VI. 



ence, it does not become necessary to add a morphological 

 increment to the nerve end organs each time the functional 

 powers of the se7ise is increased ; for just as the trained eye can 

 separate the component colors and forms and correctly judge of 

 their relations in a picture, or as the trained nose can sepa- 

 rate the several odors of a compound perfume and may cor- 

 rectly judge of the relative proportions in which the ingredients 

 are mixed, unaided by any other sense, or just as the trained 

 ear can resolve a musical chord into its notes without having 

 gained during the training any morphological increment in the 

 end organ ; so it is entirely possible to build up the complex 

 auditory function of a bird, for example, without modifying the 

 structure of the end organ in any considerable degree. In 

 this direction we may look for the explanation of the wonderful 

 acoustic powers of the thrushes with their undifferentiated coch- 

 lear organs. 



It certainly cannot be true, as Paul Meyer states, that the 

 macula utriculi is the only acoustic organ of his " pars superior," 

 nor that it is in any sense the physiological centre of this group 

 of sense organs. 



The sacculus, although belonging to the pars inferior auct., 

 has never been the subject of experimentation, as have the 

 canals, utriculus and cochlea. Its function has always been 

 assumed to be that of the perception of noises, in common with 

 the utriculus. So far as its morphological relations are con- 

 cerned, it is perfectly evident that its function in any given 

 group of animals must be practically identical with that of the 

 utriculus, unless — and here is the density of our ignorance 

 exposed — unless the central end connections in the case of the 

 two organs are so different as to cause different psycho-physio- 

 logical phenomena from identical stimuli. I think the nerve 

 connections indicate the latter view as nearer the truth. 



As for the larger question of the function of the utriculo- 

 saccular organs and their derivatives throughout the vertebrate 

 series, Milne-Edwards grasped the subject in its entirety and 

 pointed out the only possible way to a solution many years ago. 

 He said, in his great storehouse of facts {loc. cit. p. ^6 et seq.) : 

 " Ainsi que je I'ai deja dit, les Poissons sont egalement depourvus 

 de la portion cochlienne de I'oreille interne, dont le role parait 

 etre des plus importants chez les Vertebres dans I'appreciation 



