LABYRINTH OF CESTRACION AND E.HINA. 441 



in the cartilage, 4 mm. in breadth, to whose anterior wall it was 

 firmly attached by the perichondrium. After passing through 

 the skull, it made the usual bend forwards for about 5 mm. 

 Here I believe it ended abruptly, as, though looked for care- 

 fully, the duct was not traced further nor was any external 

 aperture found. The recessus only communicated directly with 

 tbe utricle above. 



The anterior utricle communicated with the saccule by a small 

 opening (canalis utriculo-saccularis anterior). The posterior 

 utricle had a similar small opening into the saccule (c. utric- 

 sacc. posterior). 



The nerves to the ampullse of the anterior and external 

 canals were long, and those to all the ampullye large. IN'erves 

 sxipplyiog tlie recessus, sacculus, and lagena were not found, 

 and were probably of minute size. 



The outer face of the saccule and lagena was directed out- 

 wards and forwards at an angle of 45° to the mesial plaae. 



Rhina squatina. Fam. Ehinidse. 



Although the membranous labyrinth of this somewhat E,ay- 

 like Sbark has been figured and described by Eetzius, yet I can 

 nowhere find any account of a feature which is most remarkable 

 and, so far as I am aware, unique in the Vertebrata — namely, a 

 complete absence of otoconia, its place being taken by sand- 

 grains introduced from without through the comparatively large 

 external opening of the ductus endolymphaticus. The sand is 

 often partly cemented into a thin plate that occupies the side of 

 the saccular cavity next the macula, but elsewhere lies loose. 

 This remarkable feature has been always found in the five or 

 six specimens bitherto examined by me ; but as it might be 

 thought that otoconia had been got rid of through the same 

 passage, I thought it well to examine a mature young before 

 birth, whicb measured 190 mm. in length. The head was 

 bisected, and all the tissues removed that surrounded the periotic 

 capsule. This capsule with its contents was then divided, and 

 the two halves of the saccule removed and examined under the 

 microscope : no otoconia were found. As it might be thought 

 that they were not present in other unborn Sharks, the unborn 

 young of Acanthias vulgaris of similar length was examined ; 

 its saccule contained abundance of large crystalline otoconial 

 particles. 



