1 8 AYERS. [Vol. VI. 



utriculo-saccular wall that is present in Myxine. An examina- 

 tion of the type figure for the Cyclostome ear (PL IX, Fig. 2) 

 well illustrates the character and extent of the difference be- 

 tween Myxine and Petromyzon in this respect. The semicir- 

 cular arch of Myxine is, then, composed of the anterior and 

 posterior vertical canals of the Gnathostome vertebrate ear. It 

 is hardly necessary to add that the argument of degeneration 

 based in part on this peculiarity of the internal ear of the Hag- 

 fish is not sustained by the facts in the case. Retzius states 

 that if the single canal of Myxine is homologous with any part 

 of the higher vertebrate ear, it must be with the utriculus (ac- 

 cording to the old conception of the extent of this chamber). 

 Retzius says that it cannot be the equivalent of the vertical 

 canals of other forms. Of the third or external canal Retzius 

 was likewise led to conclude that not a trace of it is present ; 

 but just as in higher forms the macula neglecta or abortiva does 

 not develop a canal and ampulla, although it has its discreet 

 nerve branch, so here, although ampulla and canal are not devel- 

 oped, still the sense organ is in some degree separated from its 

 parent, the anterior ampullar organ, for it receives a discreet 

 branch of the ampullar nerve, and relying upon the nerve dis- 

 tribution there are in Myxine as in Pe- 

 tromyzon indications of the future sec- 

 ondary canals. The endolymphatic duct 

 is present and sometimes bifurcates in its 

 distal portion. This bifurcation is prob- 

 ably a remnant of a previous double con- 



C«^5. — The right inter- ^^^^^O^- 



nal ear of a Lamper Eel The cauals m the Lamper Eel are well 

 {Petromyzon fluviatilis) , developed, but on account of their close 



viewed from its inner or cere- application tO the SUrfaCC of the Utriculo- 

 bral face. The figure after i ^i l. l. 



^ ^ . ,. sacculus they are not apparent as sep- 



Retzius. ac, auditory nerve; ■> ^ ^ _ '- 



<r, anterior canal; c/, poste- aratc canals from the outsidc. In order 

 rior canal; n, ramus utricu- to arrive at an adequate knowledge of 

 lans; np, ramus saccularis; their sizc, shape, and mutual relations, 



u, utriculus; up, sacculus; ... ^ .^ ^ .^y • j.- 



, , ' , J it IS necessary to study them m sections 



s, ductus et sacculus endo- -' ■' 



lymphaticus. of the ear. They are, however, fully 



separated from the utriculus and sac- 

 culus for at least part of their length, and in the large Lamprey 

 one is able to pass a sound between the canal and main chamber 



