414 



Mr. H. J. Watt. 



convex, 6 ; sharp but concave, 5 ; sharp, 4 ; medium, 3 ; flat, 2 ; very flat, 1 ; 

 then there is a correlation of +0482 + 0-071 between these values and the 

 ratio of the diameter of the second whorl to that of the first. This correlation 

 is a practical certainty, though not quite decided (i.e. > +0-50). The sharp 

 cochlea has the second whorl relatively wide. A better basis of correlation 

 would probably have been a measurement of the real height of the cochlea, 

 i.e. the vertical distance from the level of the under edge of the lowest whorl 

 to the apex of the organ. 



We may sum up the data and conclusions thus far by saying that the 

 cochlea is built according to a constant plan, of which the scale alone varies 

 from case to case. This scale shows a decidedly high correlation with the 

 size of the organism as a whole. A change of scale will obviously alter all 

 the dimensions recorded except the number of whorls. But even that 

 number, when it varies independently, does not alter the other dimensions of 

 the cochlea. The only other variant thus far detected is the rate of curvature 

 of the spiral, which is greater in the bigger scale organs. 



Fig. 3 shows graphically the relation between the various dimensions of 

 the cochlea on the principle of moving averages. The serial arrangement of 

 the organs follows the increase of the diameter of the lowest whorl. The 

 five lowest values were averaged ; then the lowest was omitted and the sixth 

 value in order of size was taken up instead, and the resulting group of five 

 values was averaged ; and so on, through the whole series. 



8. For the cochlea of birds Gray gives the measurements of 17 organs of 

 different species. The coefficients of correlation between the three series of 

 measurements given, the major axis of the oval window, the diameter of the 

 tube of the cochlea, and the length of the tube (i.e. including the lagena), 

 appear in Table II. The values are not so high as those of Table I, but there 

 is a clear correlation between the major axis of the oval window and the 

 length of the tube of the cochlea. 



Table II.— The Cochlea of Birds (17 Organs). 





Length of tube 

 of cochlea. 



Diameter of tube 

 of cochlea. 



Major axis of oval window - 754 ± '070 

 Diameter of tube of cochlea ... '508 ± '121 



•600 ± -104 



For the reptiles and amphibians Gray gives the measurements of only four 

 or five organs. One of these — the black pointed teguixin — is clearly of the 

 avian type. This group is distinguished, as Gray says, only by a shorter 

 cochlear tube. It is too small to be treated statistically. 



