THE OLFACTORY NERVE OF LEPIDOSTEUS 



117 



anterior of these two sections (fig. 4), which shows the ventral 

 ramus cut obliquely in the distal portion of its extent, contains the 

 greater number of cells. As in the previous stage, they are in 

 close proximity to the surface of the placode. This section and the 

 next anterior to it show a slight disturbance of the general epithe- 

 lial arrangement of the cells within the placode adjacent to the 



\ NEURAL TUBE 







-o ^ 





Fig. 3 Transverse section at 148 hours from fertilization, with cells in the 

 ventral ramus of the olfactory nerve. X 400. 



origin of the ventral ramus. This might be interpreted as indi- 

 cating a migration of the placodal cells into the ventral ramus. 

 Blood vessels are in close proximity to the ganglion (fig. 4). 



Six hours later, at the age of 160 hours from fertilization, a 

 greater number of cells can be seen along the distal portion of the 

 ventral ramus (figs. 6 and 7) . Two facts are to be noted especially. 

 The first is that some cells are slightly larger than those within 

 the placode and are located among the distal olfactory fibers 

 (fig. 6) as if they had migrated from the placode. The second is 



