34^5 Journal of Comparative Neurology. 



soon terminate. The axones, however, can frequently be 

 traced a considerable distance toward the exit of the optic 

 nerve. This type of ganglion cell is the most mature and the 

 largest of any found at this age. (2) A second type and by 

 far the most numerous is represented in Fig. 36, It consists of 

 a well rounded cell with but a single process. This process is 

 the axone and can frequently be traced until it is lost among 

 the other axones forming the optic nerve. This observation 

 accords with the results of His (20). He says that the axis 

 cylinder processes are the first to form in "motor cells" and 

 that the protoplasmic processes are formed considerably later. 

 (3) The third type of ganglion cells is the most immature of 

 any. It is slightly smaller than either of the other kinds and 

 possesses neither axones nor dendrites (Fig. 37). They are found 

 scattered throughout the ganglion cell layer and at this stage 

 are almost as numerous as the second type. I may be mis- 

 taken in calling them ganglion cells, for cells similar to these 

 are found in the adult. Furthermore, they correspond very 

 closely in size and shape to the cells of the original optic stalk 

 found in the optic nerve. They might thus be considered 

 homologous with them. This agrees with Cajal's results (22). 

 He says that in the optic nerve, perhaps also in the nerve fiber 

 layer of the retina of all vertebrates, spindle shaped cells are 

 found more or less isolated between the nerve fibers. There is 

 no doubt in my mind that some of these should be placed in 

 the same category with the optic stalk cell. But, since the 

 number of these cells which do not possess axones has de- 

 creased in the adult, we must assume that some of them do 

 later develop axonic processes. These three kinds of gangli- 

 onic ceils have no special grouping or location, but are found 

 variously located throughout the region of the ganglion cell 

 layer. 



The nerve fibers do not form a layer. Each fiber passes 

 from its cell of origin almost directly toward the exit of the 

 optic nerve. Nerve fibers can thus be seen going in almost 

 any direction through the ganglion cell layer. That is, a gang- 

 lion cell may be so orientated as to send the axone toward the 



