446 Rot/al Society. 



which throughout had maintained apparent contact with it, vanished. 

 The conclusion, that the dark cloud served the purpose of a con- 

 ductor and fed the zone drawing off the matter of the aurora from 

 the north, seemed to the author inevitable. The cloud did not ap- 

 pear to him to be more than forty or fifty miles distant. In conclu- 

 sion he remarks that none of the prismatic tints were observable on 

 this occasion. 



2. " On the Development of the Retina and Optic Nerve, and of 

 the Membranous Labyrinth and Auditory Nerve." By Henry Gray, 

 Esq., M.R.C.S. Communicated by William Bowman, Esq., F.R.S., 

 &c. 



The author has divided the observations contained in this paper 

 into two parts: — the first of which treats of "The Development of 

 the Retina and Optic Nerve ; the second, of the Development of 

 the Membranous Labyrinth and Auditory Nerve." 



Li the observations on the development of the retina, which have 

 been made on the embryo of the chick, the author demonstrates its 

 mode of evolution, and also the mode of development of the various 

 layers of which this membrane is formed. They commence at the 

 early period of the thirty-third hour of incubation, at which time 

 the cephalic extremity of the embryo presents a slight protrusion of 

 its walls, which by the thirty-sixth hour is very considerably in- 

 creased, having become more elongated and protruded outwards, 

 presenting a somewhat dilated end, and being somewhat constricted 

 at its connection with the anterior cerebral cell from which it arises. 

 This is the first indication of the development of this membrane. 



At the forty-sixth hour this protrusion (which the author calls 

 the optic vesicle) was still more distinct, and the cavity in the cere- 

 bral cell, from the wall of which it arises, was well seen, and it was 

 observed to communicate with the cavity of the optic vesicle which 

 was also hollow. This description of the mode of development of 

 the retina the author considers as confirmatory of the observations 

 made by Baer, but not in accordance with that given by Wagner 

 or Huschke. 



The author then proceeds to detail very minutely the consecutive 

 stages of the development of the retina and parts in immediate con- 

 nection with it, until the seventh day, when he states that on making 

 a section of the eye, it was separated from the other tunics as a per- 

 fectly distinct layer. The optic nerves were also now completely 

 formed, being united to form the chiasma, and passed inwards in 

 the direction of the under surfiace of the corpora quadrigemina. 



The author in the next place proceeds to consider the develop- 

 ment of the various layers of the retinal membrane, a point which 

 appears not to have been previously noticed by any physiologist. 

 This membrane on the eighth day of incubation can be seen, by the 

 naked eye, distinct from the other tunics. Its choroidal surface is 

 composed of a mass of globular nuclei about the size of the red cor- 

 puscles of the blood, which form at this period about one-half the 

 entire thickness of the retina, the deeper surface consisting of some 

 fine granular n^atter and a mas^ of pale and delicate nucleated cells 



