354 Journal of Comparative Neurology. 



The retina of the adult mole very closely resembles that of 

 the young. In many cases it completely fills the vitreous 

 chamber. In others a small vitreous chamber is found (Fig. 9, 

 10 and 13). In cross sections one frequently finds a space 

 between the retina and the pigment layer (Fig. 18, s). This 

 is an abnormal occurrence and was caused by the preserving 

 fluids. 



The different layers of the retina appear distinct and of 

 almost uniform thickness. In many cases the ganglion cell 

 and nerve fiber layers have been reduced to a mass occupying 

 the center of the eye and immediately in contact with the lens 

 (Fig. 14). These two layers are so confused that they are no 

 longer distinguished as two distinct layers. When a vitreous 

 chamber is present the ganglion cells and nerve fibers are 

 spread out into a more or less uniform layer (Fig. 13). A 

 transitional form between these two extremes is represented in 

 Fig. 18. Here the pencil-like vitreous chamber prevents the 

 inner surface of the ganglion cell and nerve fiber layers from 

 uniting and thus forming a mass. This condition is no doubt 

 brought about by the growth of the retina much more rapidly 

 than the sclerotic coat. It is thus confined in a smaller space 

 than in a normal eye and conforms to this space in a variety of 

 foldings and arrangements. All the layers of the retina show 

 this crowded condition to a greater or less extent. 



All the elements of the normal mammc'lian retina are 

 found in the eye of the adult. Owing to the crowded condi- 

 tion of the retina these elements are not arranged in a normal 

 manner. It is my belief that if the adult mole retina were 

 spread out over a surface bearing the same ratio to the size of 

 the body as obtains in other mammals the retina would be sim- 

 ilar to that of the normal animal. The mass and number of 

 elements present seem to substantiate this belief. No measure- 

 ments have been made to test the validity of this supposition. 



The thickness of the retina varies with different individ- 

 uals and with different hardening fluids. Table 3 gives the 

 thickness of the retina and its layers when hardened in the 



