NERVUS TERMINALIS IN AMI A 71 



along the developing oculomotor nerve, while in the case of the 

 nervus terminalis the migration is from the placode toward the 

 neural tube. 



The nuclei of the ganglion on the olfactory nerve of Amia, can 

 be distinguished readily from the nuclei of the sheath cells or of 

 surrounding mesodermic elements when the young are about 

 10 mm. to 12 mm. long. These nuclei are larger than any others 

 near them and are situated on the ventro-median side, as Allis, 

 ('97) described them, about midway between the outer wall of 

 the neural tube and the olfactory cup. There are perhaps two 

 dozen nuclei on each olfactory nerve at this stage. The capsule 

 which Allis describes as surrounding the ganglion has not been 

 very evident to me, but there are smaller cells partly surround- 

 ing it on the side next the olfactory nerve, which I have taken 

 for sheath cells of the olfactory nerve. 



The ganglion increases in size and number of cells, but generally 

 remains a single compact mass until about the 25 mm. to 30 mm. 

 stage. In a few cases its cells have been found distributed in two 

 or three aggregations along the olfactory nerve. It keeps its 

 position about midway between the anterior end of the brain 

 (bulbus olfactorius) and the most rostral part of the developing 

 nasal capsule. The olfactory nerve is lengthening at this time 

 and. the brain lies farther caudad with respect to the eyes and 

 some other structures when the fish has grown to maturity, and 

 as Allis ('97) states, the olfactorj^ nerve in the adult is about 

 one and one half times as long as the brain. From the first ap- 

 pearance of the ganglion it is located near the point where a 

 branch of the external carotid artery joins the olfactory nerve 

 to be distributed to the nasal capsule. 



When the young of Amia are from 25 mm. to 30 mm. in length, 

 some of the cells, of which there are about forty at this stage, 

 have wandered rostrad from the main ganglion and are scattered 

 among the peripheral olfactory fibers. There are some five or 

 six folds in the mucous membrane at this stage in each of two 

 series lying one on either side of a median fold or " mid-rib" in 

 each nasal capsule. Earlier the opening of each nasal capsule to 

 the outside was a slit which has now closed in the middle to pro- 



