On the Perilymphatic Spaces of the Aiii[)hil)ian Ear. 253 



SO low down in the scale that the pars basilaris has come to form the 

 most important constituent of the cochlea in the higher Vertebrata. 

 The lagena, less favourably situated with regard to the perilymphatic 

 spaces, has suffered eclipse. As to the pars neglecta, which in both 

 Urodela and Anura, has close relations with the perilymphatic system, 

 its want of success is perhaps due to the situation of its macula on a 

 part of the wall separating sacculus and utriculus — a position much 

 less favourable to independent and progressive evolution than that oc- 

 cupied by the freelj^ projecting pars basilaris. 



It may seem that I have attached undue importance to the system 

 treated of in this paper. I believe however that the evidence I have 

 brought forward all tends to enhance the significance of the system, 

 both from the physiological and the morphological points of view. Its 

 function, by virtue of the contained perilymph, as an intermediary be- 

 tween the membranes closing the apertures in the auditory capsule and 

 the sensory areas of the labyrinth, is rendered still more obvious when 

 we recognise that the labyrinth itself possesses diaphragm-like areas, 

 separating perilymph from endolymph. Its inhibitory influence on the 

 process of chondrification of the auditory capsule over certain areas 

 affords us an explanation of morphological features otherwise inexpli- 

 cable. We can recognise in a general way an interaction between a 

 tendency towards greater physiological efficiency on the one hand, 

 and the inertia of pre-existing structure on the other. At the same 

 time, it seems probable that "accident" has played a part of some im- 

 portance, giving rise to relationships which have undergone structural 

 adjustment in the interests of function. 



V. Summary and Conclusions, 



1. The space between the walls of the auditory capsule and the 

 membranous labyrinth in the Amphibia is occupied partly by connec- 

 tive tissue (jjerilymphatic tissue), and partly by definite, constant, and 

 restricted spaces (perilymphatic spaces) containing the perilymph. In 

 the Urodela the spaces are three in number, and are applied to certain 

 areas {tympanal areas) of the walls of the sacculus, pars neglecta, and 

 pars basilaris respectively. 



