14 AYERS. [Vol. VI. 



size, the shape, the position of the parts of the canalar arch 

 with respect to the tliree planes of space are subject to exten- 

 sive variation. 



We have just seen the character and degree of these varia- 

 tions in Torpedo. I can do no more here than to state that 

 every species of vertebrate has its own pecuUar variation above 

 and beyond the individual differences. As regards the length 

 of the canals, they vary from about i mm. in length, as in the 

 smaller species, especially of the higher vertebrates, to 13 cm., 



as in the case of a shark meas- 

 uring seven feet in length. In 

 our recent sharks the canals do 

 not, perhaps, exceed 20 cm. in 

 length in any case. In the seven- 

 foot shark, with canals 13 cm. in 

 length, the largest teeth meas- 

 ured only one inch across the 

 base. In nearly related extinct 

 forms with teeth measuring five 

 inches across the base, if the 

 Cm/j.— A projection of the hori- same proportion held good be- 



zontal canal of the same ear on the ^^^^^ ^j^^-j. ^^^^^ ^^^ ^gg^j^ 

 sagittal plane, to show its relation to . 



the horizontal plane. measurements, — and there is 



every reason to suppose that 

 such was the case, — these enormous extinct forms must have 

 had canals at least 65 cm. in length. That such angular 

 variations from the commonly understood relations of the 

 canals, as I have described, are of frequent occurrence has 

 long been known, but not much, if any, allowance has been 

 made for the almost universal failure of the canals to come up 

 to the theoretical standard, and no notice has been taken of the 

 very much modified type by the speculative physiologist. Hasse 

 described in 1868 (117) the frog's ear canals in great detail. 

 He found that the external canal projects upward from the 

 horizontal plane at an angle of from 40° to 55°, and the anterior 

 and posterior canals are nearly as much out of the sagittal and 

 transverse planes. Hasse had already pointed out the general 

 law, that the ampullae and the canals are placed obliquely to the 

 planes, whose names they bear, and he says further {loc. cit. p. 12), 

 " Es ist demnach nicht vollkommen richtig, wenn wir von 



