344 Journal of Comparative Neurology. 



the light no longer enters the eye, or at best only in a very 

 obscure way. 



The retina at this age practically fills the whole of the 

 vitreous chamber. In sections of the eye the retina is fre- 

 quently found more or less separated from the pigment and 

 choroid layers. This is an abnormal condition and due to the 

 action of the hardening fluids. Sometimes in the region of 

 the entrance of the optic nerve a small space is observed which 

 is the remnant of the vitreous chamber. 



The principal layers of the retina are generally easily 

 discerned, but owing to the apparent shrunken condition of the 

 sclerotic the cells composing these layers are very much crowd- 

 ed. This is especially true of the ganglion cells. 



All the elements of the retina at this age have been 

 observed, with the possible exception of the rods and cones. 

 I have not been able to demonstrate them with certainty in any 

 of the specimens I have examined. The processes of the 

 pigment cells are easily seen in places and might be mistaken 

 for rods and cones. If they are present, they are in a much 

 more rudimentary condition than that described by Kohl in 

 the European mole of this age. He describes them as easily 

 seen and about half as long as those in the adult. The imma- 

 ture development of the processes of the outer nuclear cells 

 leads me to say that the rods and cones have not developed at 

 birth. 



The outer nuclei present an immature condition. They 

 appear as elliptical cells and measure on an average .0036 

 mm. by .0100 mm. (Fig. 40). Processes are observed to 

 start from these cells, but I have been unable to trace them 

 any great distance. In no case have I been able to follow 

 them into an enlargement which might be considered a devel- 

 ing rod or cone. The fault may lie in the method of staining. 

 These cells form a well defined layer about five cells deep which 

 averages .0225 mm. in thickness. It forms a continuous 

 layer from the lens on one side around to the lens on the other. 

 In the region of the lens these cells are not sharply separated 

 by the outer molecular layer from those of the inner nuclear 



