915 



is an offset. The vesicle was hollow, clear and pellucid, and of a 

 flattened circular form. At the fifty-sixth hour it had increased in 

 size and presented a pear-shaped figure ; so that now the narrow 

 contracted tubular portion appeared the first stage in the develop- 

 ment of the auditory nerve ; the dilated portion, the auditory sac or 

 rudimentary vestibule ; and the cavity still existing in its interior 

 and communicating with the ventricular cavity from which it arises, 

 by means of the tubular prolongation, the auditory nerve. The 

 aperture of communication soon becomes smaller and more con- 

 tracted, and this increases as the separation between the auditory 

 vesicle and its parent-cell takes place. At the sixty-fifth hour, be- 

 sides a great increase in the size of the ear-bulb, the auditory nerve 

 has become more distinctly formed, and is quite solidified, so 

 that no communication can now be traced between the ventricular 

 cavity and the vestibular sac. It is in this stage of the development 

 of the auditory apparatus that a great similarity is to be observed 

 between it and the normal condition of the same part in some of 

 the lower animals. There are, in fact, now formed the two element- 

 ary portions of the auditory apparatus, the auditory nerve and the 

 simple vestibular sac. Such is the simple condition of the organ in 

 the Crustacea and Cephalopod MoUusks. At the seventy-second 

 hour, the vestibular sac has lost its oval form and presents a con- 

 traction around its entire circumference. This is the first indication 

 of the separation of the vestibule from the membranous semicircular 

 canals which are ultimately formed from the terminal portion of the 

 vesicle. 



The minute examination of the development of these structures, 

 of which a consecutive detail is given, leads the author to remark 

 on the almost precise similarity in structure of the membranous 

 labyrinth to the retina in its various stages of development, for it 

 consists like it of a delicate fibrous mesh in the areol[3e of which is 

 deposited granular matter and numerous nucleated cells, its outer 

 surface being composed of globular-shaped nuclei arranged similar 

 to those covering the outer surface of the retina at an early period 

 of its development. 



From this description a marked similarity may be observed be- 

 tween the origin of this membrane and that of the retina. In both 

 cases they arise as a protruded portion of the cerebral mass, being 

 hollow and communicating with the cavity of the parent-cell. In 

 process of time, a gradual separation takes place between them and 

 the parts from whence they arise. They then assume a pyriforni 

 shape, but still communicate with the cerebral cavity. As, however, 

 the nerves become solidified and the separation between them is 

 more fully effected, then no communication can be traced between 

 the two cavities. 



3. "Tide Researches. Fourteenth Series. On the Results of 

 continued Tide Observations at several places on the British Coasts." 

 By the Rev. W. Whewell, D.D., F.R.S. Sec. 



Tide observations made at several different parts of the British 



2* 



