198 MARINE BIOLOGICAL LABORATORY. 



lymphatic duct (s), and the duct itself into two quite 

 symmetrical portions. The anterior corresponds to the 

 anterior part of the Torpedo ear, and there is a similar 

 correspondence between the posterior halves of these 

 two ears. The main points of difference are, ist, The 

 sense-organs of the Myxine ear are only three in num- 

 ber, or at most four. 2d, The canals, only two in 

 number, and they do not communicate by their amal 

 ends with the main sac of the ear, or the utriculo- 

 sacculus, for here the chambers are not separated 

 though distinctly marked off. 3d, The endolymphatic 

 duct does not communicate in the adult with the sur- 

 face of the body. 



The auditory nerve, however, has the same number 

 of divisions, — two, — and they supply the utriculus with 

 its anterior ampulla, and sacculus with its posterior am- 

 pulla, respectively, the same as in the Torpedo ear. 



Fig. 3. — The right internal ear of a Lamper-eel 

 (^Peti'omyzon Jluviatilis), viewed from its inner 

 or cerebral face. The figure after Retzius. 



ac Auditory nerve. n Utriculus. 



c Anterior canal. up Sacculus. 



cp Posterior canal. s Ductus et sacculus endo- 

 n Ramus utricularis. lymphaticus. 



oc' " tip Ramus saccularis. 



In Petromyzoji the ear is much more compact than 

 in any other known form ; the canals, though two in 

 number and well developed, do not rise above the sur- 

 face of the utriculo-sacculus ; and although they fuse 

 together at their proximal ends as in Myxine, they also 

 open into the main sac by a short, small tube. The 

 whole structure is divisible by a vertical passing through 

 the apex and the middle of its base into anterior and 



