1 34 AYERS. [Vol. VI. 



vesicle into an upper, inner, anterior chamber, — the utriculus, 

 and lower, outer, posterior chamber, — the sacculus. 



When fully formed this partition runs obliquely across the 

 auditory vesicle, and as the ear approaches its adult conditions, 

 grows more and more oblique to the original axis of the vesicle. 

 The semicircular canals of the Frog form, in the manner already 

 described, for the surface canals in Amia and the auditory canals 

 of the Elasmobranchs and Teleosts. 



Relative to the time of appearance there are variations worthy 

 of mention. The anterior and the external canals develop 

 simultaneously, while the posterior is perfected only later. 

 Nevertheless, the sense organ of the latter canal is cut off from 

 the macula sacculi before those of the anterior and external canals 

 are formed. Villy adopts the view that, on account of the later 

 development of canalis posterioris, the older idea that the two 

 vertical canals are older structures is not correct. The posterior 

 canal appears before the folds of the other canals have united, 

 and it forms exactly like the others. The two vertical canals 

 continue to grow until they meet and their two half-pores unite 

 into a primary pore, which opens on the inner surface of the 

 utriculo-sacculus. On account of the late appearance of the 

 posterior, canal, Villy unfortunately concluded that the deduc- 

 tion from the comparative anatomical evidence bearing on the 

 case, which holds the Cyclostome ear to be an ancestral struc- 

 ture, from which the Gnathostome vertebrates have derived their 

 auditory organ, to have insufficient foundation ; and he says 

 {loc. cit. p. 529), "This doctrine is very much shaken by the 

 results arrived at in this paper." Villy distinctly says that the 

 early appearance of the sense organ cannot be considered as 

 showing that the posterior canal forms first. In this view he 

 shows that he has totally failed to appreciate the significance of 

 the relation existing between the sense organ and its canal. 



Our author says (p. 532) : "The fact that this epithelial tract 

 is the first to develop might be taken to show that though the 

 posterior vertical canal actually forms later than the others, 

 nevertheless it is indicated earlier than they are. This early 

 specialization may, however, possibly be explained as a con- 

 venience due to the out-of-the-way position occupied by the 

 organ concerned, and to the early formation of the septum 

 between the utriculus and sacculus, which in its growth plays 



