NERVUS TERMINALIS IN AMIA 



65 



irregularly at the outer margin of the capsule. These irregularly 

 arranged nuclei form a continuous series with the nuclei within 

 the olfactory nerve, which have migrated out of the placode. At 

 this time these nuclei appear to be nuclei of indifferent cells 

 that are migrating along the olfactory nerve. Probably they 

 are of the same general nature as the nuclei producing the susten- 

 tacular cells of the nasal epithelium. Later the larger part of 

 these nuclei along the olfactory nerve produce sheath cells for 



Fig. 5. Horizontal section of Amia about 30 hours after hatching. Shows 

 growth in length of the olfactory nerve. Nuclei are migrating from the placode 

 along the olfactory nerve. Note the position of the blood vessel at the anterior 

 side of the olfactory nerve. Stained in thionin and acid fuchsin. X 400. 



the olfactory fibers. They are more numerous peripherally than 

 in previous stages, but disappear entirely just before the brain 

 wall is reached. Inside the brain there is a fiber zone, as was 

 the case earlier, that is devoid of nuclei (fig. 5) . The mesodermal 

 elements are closely crowded about the outside of the connective 

 tissue sheath which is seen at the outer border of the nerve 

 peripherally where it is continuous with the sheath around the 

 nasal capsule. Where this sheath is present the mesodermal 



