1/6 



AVERS. 



[Vol. VI. 



empty into the upper part of the vesicle or the utriculus are 

 more distinctly marked off from the vesicle, and each presents 

 at both its ends an enlargement, one of which contains a nerve 

 end organ or a portion of the auditory sense apparatus. This 

 is the so-called ampulla. 



The other enlargement is non-nervous, and is the pseudo- 

 ampulla, or, as I shall designate it, the Ama. With the forma- 

 tion of the three canals, their ampullae and amae, the cochlear 

 canal and the more sharply defined separation of the utriculus 



Cut j8. — The head of the 

 embryo Smooth Dogfish 

 (^Galeus canis), seen from 

 the left side. Figure drawn 

 from nature, magnified 

 about 20 times. The 

 flask-shaped auditory vesi- 

 cle is shown prominently 

 placed above the gill re- 

 gion. Letters as in the 

 preceding figure. 



Cut ig. — The head of an older Shark 

 of the same species, viewed from the 

 left side. The figure, which was 

 drawn from the living fish, shows 

 the internal ear well advanced in its 

 development. The rudiments of the 

 semicircular canals and lagena are 

 seen pushing out from the auditory 

 sac (respectively the utriculo-sac- 

 culus, which has sunk far below the 

 surface, with which it is, however, 

 still connected by its sickle-shaped 

 ductus endolymphaticus). 



a.v Auditory vesicle. 

 c Anterior canal. 

 d Ductus endolymphat- 

 icus. 

 e Eye. 

 f Fore-brain. 

 ch External canal. 



cp Posterior canal. 



/ Lagena. 



m Mid-brain. 



h Hind-brain. 



11 Nose. 



u Umbilical cord. 



from the sacculus, the Shark ear assumes the conditions and 

 proportions which characterize it in the adult. The ductus en- 

 dolymphaticus retains its connection with the exterior through- 

 out life, and places the internal ear in communication with the 



