No. I.] THE VERTEBRATE EAR. 223 



exact semicircular shape is the usual form of these canals, for 

 such is far from being the case, and I have very great doubts 

 that the mathematically accurate canal, or even a near approach 

 to it, ever occurs in the w^hole vertebrate group. Usually 

 the canals have the shape of segments of ellipses, parabolas, or 

 hyperbolas ; when simple or when complex or irregular, a repeti- 

 tion of one or more of these curves. As has often been noted, 

 the canals do not lie in the plane passing through the centre of 

 the two ends and the centre of the middle portion (usually the 

 apex) of the curve, but quite frequently one half the curve lies 

 above, the other below, this plane. In man this is regularly so. 

 In the bird the canals appear to be much more perfectly semi- 

 circular than in any other group save some of the fishes. 



The canals do not even form about the same patch of sensory 

 cells. For, according to some observations on the embryo fish 

 and amphibian, the posterior canal originates about the cochlear 

 patch of cells, while the anterior arises about a part of the 

 utricular patch, the horizontal in its turn being formed by a 

 division of the anterior sense organ. The adult ear preserves 

 traces of this mode of development, as members of every verte- 

 brate group whose anatomy has been studied clearly prove. 

 In Myxine we have the simplest condition, the posterior canal, 

 arising from the end of the vesicle opposite to the anterior 

 canal, the former innervated by the cochlear, the latter by the 

 vestibular branch of the auditory nerve. Between Myxine and 

 the Elasmobranch the anterior canal organ divided, giving off 

 the external canal organ. The saccular organ became separated 

 from the utricular, but its offspring, the posterior canal organ, 

 remained within the saccular territory. The cochlear organ, 

 later, divides again. I have not yet worked out the full 

 details of the development of the sensory patches of the ear 

 above the fishes, but there can be no doubt that they all arise 

 in the typical manner now known for the most important audi- 

 tory sense organs. From the phylogenetic standpoint, then, 

 the ear canals, both in their development and in their adult 

 condition, certify to descent from surface canals ; or strictly 

 speaking, they conclusively shozv themselves to be the sw'face 

 canals of a submerged superficial area, zvJiich, owing to its i7tore 

 or less flask-like form, permits only a mediate communication of 

 its cajials with the circumnatant fluid. Even this communica- 



