1^8 A VERS. [Vol. VI. 



the surface of the head and caused to spread itself out flat. The 

 inner face of its wall would thus form the surface of the head 

 over the area covered. The canals would then appear as surface 

 canals arranged somewhat as is shown in Cut 20. Here we 

 find the canals inclined at varying angles to the long axis of 

 the body. They form a group such as one may find on the head 

 of any fish having the canal organs well developed; i.e. there 

 is no essential difference between the relations of the parts as 

 here projected and the canal organs on the surface of the body. 



The De'velopvient of the Ear in Ganoids and Teleosts. 



Salensky describes the development of the Sturgeon ear as 

 follows {lac. cit. p. 307) : — 



" L'organe de I'oui'e, qui apparait assez tot, est represente par 

 les otocystes, situes de chaque cote de la moelle allongee, et 

 resultant d'une invagination de la couche inferieure de I'exo- 

 derme. II est probable que cette couche s'epaissit prealable- 

 ment, car, apres la formation des fossettes auditives, nous la 

 trouvons plus epaisse autour de I'orifice de ces dernieres. Deja 

 avant sa transformation en otocyste, la fossette auditive est pyri- 

 forme. Ses parois formees de cellules cylindriques sont epaisses 

 dans le fond de la depression, et sa cavite a la forme d'une fente 

 triangulaire." "Vers la fin du developpement, l'organe de I'oui'e 

 a la forme d'une vesicule ovalaire, a parois assez minces formees 

 de cellule cylindriques. Sous cet aspect, il represente I'ebauche 

 du labyrinthe, aux depens du quel se developperont dans la suite, 

 les recessus labyrinthi, les canaux semi-circulaires et le canal 

 cochleaire, toutes parties qui n'atteignent leur developpement 

 complet que pendent la periode post-embryonaire." 



The auditory vesicle of the bony fish arises below the surface 

 of the skin and does not present, as in the Shark, a genuine 

 involution. There is, however, at a stage antecedent to the 

 formation of the solid auditory sac, a thickening of the super- 

 ficial epithelium behind the eye over the region occupied a 

 little later by the auditory vesicle. It has not been ascertained 

 whether this epithelial thickening is a superficial sense organ 

 or not, and we know nothing of its fate or relation to the audi- 

 tory organ within the head. The outer opening of the vesicle, 

 i.e. the distal portion of the endolymphatic duct, places the cav- 



