lO AVERS. [Vol. VI. 



well as in all the higher groups, there is a varying dispropor- 

 tion, the sacculus becoming in general the larger of the two 

 chambers. 



In the Cyclostomata, as one would expect, these chambers are 

 very nearly equal in size, and in some forms are scarcely sepa- 

 rated from one another. In Dasyatis the sacculus is drawn out 

 backwards, downwards, and outwards, into a curved blind pocket 

 (/.), the lagena. The utriculus in this species does not show a 

 similar pocket, though it is well developed in some Elasmo- 

 branch fishes, and the sense-organ differentiation connected 

 with it variously indicated in many of the higher forms. The 

 anterior canal complex is made up of the two semicircular canals 

 known as the anterior {ca.) and the external {ce.), respectively, 

 their ampullae (aa.), and {ae.) the anterior and external ampullce, 

 the common ama of the two anterior canals, and the enlarge- 

 ment with which the ampullae communicate by their short 

 ampullar tubes. The posterior canal {cp.) has failed in this 

 species to produce a canal complex ; but, as we shall see, its 

 sense organ has by division produced two ampullar sense 

 organs, one of which does not develop an ampulla and canal. 

 The posterior canal, its ampulla {ap.), and the tube placing the 

 ampulla in communication with the short canal {s), are the parts 

 of the saccular canal. 



The endolymphatic duct of Dasyatis {d.) is relatively large, 

 and preserves the continuity of the lining coat of the internal 

 ear with the surface of the body from which it sprang, and thus 

 in a certain sense the superficial position of the auditory sense 

 organs. When we recall the well-known facts relative to the 

 location of the lateral line organs, — placed below the surface 

 of the skin in canals, in pits, or at the bottom of deep depres- 

 sions in the surface of the body in many species, or going still 

 further to occupy channels hollowed out in the subdermal car- 

 tilage, and more or less complete canals formed in the dermal 

 bones and scales of the body in other forms, — we perceive at 

 once that the position of the ear within the skull is different 

 from that of its relatives at or nearer the surface of the body, 

 merely m the degree of removal and the extent of the modifica- 

 tions induced by such removal from the surface. 



The utricular and saccular chambers of the Torpedo ear 

 (Fig. 3) and of the Carcharias ear (Fig. 2) are quite similar in 



