202 Journal of Comparative Neurology. 



process in many cases turns towards the ventricle instead of the 

 periphery, thus taking a reversed direction. This, however, 

 can be explained as the result of the rotation of the main pro- 

 cess, for we can see several stages in the rotation, as the figure 

 shows. The beginning of rotation is shown at (a), and cells 

 half rotated as well as those completely rotated, are easily 

 found. From this, we conclude that the main or large proces- 

 ses of the cells in the fourth layer, which show a similar char- 

 acter to those in the third layer, have really the same structure 

 and significance. The process thus rotated, however, sliows 

 quite an important morphological alteration when compared 

 with the corresponding process in the lower layers. The term- 

 inal portion of processes enlarges greatly, and finally forms a 

 somewhat triangular shaped expansion. From two extremities 

 of the basal line of the triangle, very delicate branches are pro- 

 duced, one from each end. In some cases, the secondary 

 branch enlarges again at its terminal points and forms other 

 branches. The size of the terminal enlargement is variable, as 

 will be seen from Fig. 3. Further, the processes show a some- 

 what irregular outline and have a variable calibre instead of 

 tapering gradually as do those of the third layer. The nucleus 

 in the bipolar cell is .-omewhat spherical, except in a very few 

 cases; at least it does not show the oblong shape to be seen in 

 the monopolar cells. Whether the shape of the nucleus has 

 some relation to the movement of the cell-body, we cannot 

 say positively, though such a relation is very probable. 



The question at once arises concerning the nature of the 

 process which first appears; whether it is a neuraxone or a den- 

 drite. According to the existing view, this process is the nc'u- 

 raxone because it is the first process to develop. But as will be 

 seen from the illustration, one can hardly regard it as the 

 axone, since it has none of the characters of an axone. On the 

 other hand, the terminal enlargement where two branches arise, 

 as well as the irregular outline of the process gives it all the 

 characters of a dendrite. Further, the second process which 

 arises directly from the opposite side of the cell-body favors 

 this interpretation for it shows the character of the neuraxone. 



