The Typical Form of the Cochlea and its Variations. 415 



B. The Variations in the Form of the Cochlea. — Having thus shown that 

 the mammalian cochlea is an organ of a definite type, we may enquire 

 whether there is any regularity in the way in which the cochleas of different 

 species deviate from the type. In order to ascertain this I divided each 



.Success.'ve orouos of f/'ve oroans 



Fig. 3. — Cochlea of Mammals (Moving Averages). 



measurement of each organ given by Gray (with the exception of " the slant 

 height of the cochlea ") and my estimate of the length of the basilar 

 membrane by the diameter of the lowest whorl of that organ. The resulting 

 values I may call the cochlear indexes of the organ. 



