The Typical Form of the Cochlea and its Variations. 419 



much hunted animals, while the lower group consists mainly of herbivorous, 

 insectivorous, and aquatic creatures. 



It is of interest to note how low in the scale man stands. He is asso- 

 ciated with the horse, the whale, the dromedary, the mole, the sheep, the 

 hedgehog, and the sea-cow. Whatever an increased basilar membrane 

 means functionally for hearing, whether it be a greater sensitivity or a 

 greater pitch-range of hearing, or both, man can hardly claim to have any 

 high power therein, if we may judge from the general impression of the 

 power given by his associates in this Table. Amongst Dr. Gray's photo- 

 graphs there are depicted many more regular and beautiful organs than 

 man's. Music may require a great mind and a great soul, but it can hardly 

 presuppose a very fine receptor organ. 



[16. In Table IV the positive correlation between the index of the basilar 

 membrane and the number of whorls (cf. Table III) may be seen at a 

 glance. But minor deviations from it are also apparent ; for example, one 

 might have expected the capybara with 4£ turns to have the highest 

 basilar index. And it is striking that the next organ on the list has only 

 2| turns. Obviously some other variant must have caused these " short- 

 time oscillations," so to speak. The measurements given for the capybara's 

 organ suggest a likely cause. The photograph of that organ shows a high 

 rate of curvature, the relation of the diameter of the second whorl to that 

 of the first being only 64 per cent. So I reckoned a short-time fluctuation 

 in relation to rate of curvature with the help of moving averages (groups 

 of five organs) and the modifications of Karl Pearson's formula used in 

 connection therewith, and found it to be — 0-474 + 0-083. That is very 

 nearly a decided correlation. And it indicates that an increased rate of 

 curvature calls for more whorls, a wider second whorl for fewer whorls, 

 than would generally be required by the functional demands summed 

 together in the index of the basilar membrane. 



This result might have been deduced from the results stated in Part A. 

 For if extra whorls are added on at the apex without alteration of the 

 other dimensions, the extra amount of basilar membrane required in a 

 cochlea with a wide second whorl will go into fewer turns than in a cochlea 

 with a narrow second whorl. But it is well to derive it independently, 

 for it clarifies the functional significance of the basilar index, showing it to 

 be independent of the other variable features, and helps towards a reasoned 

 understanding of the architectonic of the cochlea. — Added December, 1916.] 



17. Table V gives the ranking for the birds, if an index is taken from 

 the highest correlation — the length of the tube of the cochlea divided by 

 the major axis of the oval window. Here, again, a carnivore heads the list, 



