No. I.J THE VERTEBRATE EAR. \\ 



shape. The separation of the two chambers (Cut i) from the 

 median portion (inner end of the endolymphatic duct) is not so 

 complete and typical as in the case of the Dasyatis ear. The two 

 chambers appear as appendages of the median much-enlarged 

 portion, and their relation to the median raphe of division is 

 masked somewhat by the size and position of the median cham- 

 ber. The enlarged end of the surface canal, the so-called endo- 

 lymphatic duct, forms in these ears the utriculo-sacculus proper, 

 which is a relatively large pear-shaped or subconical sac. Its 

 walls are perforated by holes, one placed on the anterior inner 

 face, the other on the posterior inner face of the median sac. 

 The median chamber forms about one-third of the ear sac of the 

 Torpedo, and the utriculus and sacculus appear to spring out of 

 its lower anterior, inner and lower posterior, inner faces, respec- 

 tively. The stem of the pear is formed by the long endolym- 

 phatic duct, which leads off from the funnel-shaped enlargement 

 at the small end of the pear. This part corresponds to the 

 aqiiednctus vestibuli of other vertebrate forms, and is clearly the 

 basal portion of the endolymphatic duct, which, remaining undi- 

 vided, does not so openly disclose its nature as does the homol- 

 ogous part in the Sting Ray (PI. I, Fig. i). 



In the Torpedo the utricular and saccular evaginations, which 

 have resulted in the formation of the semicircular canals, com- 

 municate at three points with the auditory sac. They are 

 placed, as an inspection of Cut i shows, one near the anterior 

 border of the utriculus, one near the posterior border of the 

 sacculus, and one near the apex of the cone-shaped chamber 

 common to both the utriculus and sacculus. The first of these 

 openings is a "half-pore," as defined by Allis, and represents the 

 original pore left by the canal formed over the anterior ampullar 

 sense organ. The canal leading outwards from this pore soon 

 splits into two, one of which leads into the external ampulla. 

 This splitting of the canal was induced during development by 

 the division of the anterior ampullar sense organ, and resulted 

 in providing the offspring of the parent organ with a canal of 

 its own, which, however, does not, as in some species, acquire a 

 separate opening into the utriculus, but uses the parent canal 

 for such communication. The second opening is that of the 

 saccular ampullar organ, or that of the posterior canal, which in 



