586 SCIENCE PROGRESS 



sense organ quite accessory to the sense organ itself. For our 

 present purpose the essential things to note are (i) the tense 

 but thin basilar membrane stretched from end to end of the 

 scala media, in a rigid frame (figs. I, 2, Mbr. bas.); (2) the 

 close relations of the basilar membrane to the brain cavity 

 and the exterior through the mediation of a definite perilymph 

 space {scala tympani). 



These two characters are in fact the only ones to suggest 

 that the pars basilaris of the Amphibia is a cochlea in the 

 making. There is in this group of vertebrates no scala vestibuli 

 and no organ of Corti but there is a thin circular basilar 

 membrane framed in a cartilaginous thickening of the surround- 

 ing walls, and applied to the exposed {i.e. mesial) surface of this 

 basilar membrane is a little perilymph sac {scala tympani) 

 (fig. 3, amphibian, P. bas., Sc. tymp.) which is in close con- 

 nexion with the brain cavity and with the exterior on the one 

 hand and on the other by means of a tortuous but definite 

 tube (fig. 3, D. PLPH) with a great vestibular perilymph space 

 (Sp. sacc. fig. 3) lying between the fenestra ovalis (fig. 3, 

 f. ov) and the sacculus. At present there is no prolongation 

 of this vestibular perilymph chamber upon the outer surface 

 of the pars basilaris — no suggestion in fact of a scala vestibuli. 

 The sense organ of the pars basilaris at present lies near 

 but not upon the basilar membrane. 



In this primitive condition of the auditory organ, there are 

 none of those refined peculiarities of structure that we are 

 accustomed to associate in the cochlea of higher vertebrates 

 with a power to analyse compound musical notes. There is no 

 specialisation of the sense organ such as we see in the organ of 

 Corti, no fibred structure of the basilar membrane and no 

 regular variation in size and number of the various elements of 

 which the different parts are composed. It is thus very doubtful 

 whether we should be justified in regarding these modified 

 tympanal areas in the endolymph labyrinth of the amphibia, 

 with their associated perilymph chambers, as anything more 

 than mechanisms for focussing vibrations upon certain sensory 

 areas. 



But although we can scarcely credit amphibia, on structural 

 grounds, with a musical sense, there is every reason to suppose 

 that differences in the rapidity or complexity of the vibrations 

 beating upon the sense organs in the ear produce recognisable 



