NERVUS TERMINALIS IN AMIA 69 



olfactory nerve and a greater surface of the ganglion, whereas 

 the sections of the previously collected material were cut trans- 

 versely. At all ages the ganglion appears more striking in sagittal 

 and horizontal sections than in transverse, probably because the 

 ganglion is slightly elongated in the direction of the axis of the 

 body of the fish. 



I have searched carefully for any placode or other source of 

 origin of the nervus terminalis outside the olfactory capsule and 

 nerve, but to no purpose, although Locy ('05) describes it as 

 arising separately in Acanthias. If there is a separate placode in 

 Amia, I have not been able to recognize it unless, indeed, the 

 unpaired nasal placode already described is the beginning of the 

 nervus terminalis, for this placode is the most anterior part of the 

 nervous system I have found in Amia. In that event it would 

 have to be said that the placode of the nervus terminalis is ab- 

 sorbed into the paired olfactory placodes from which the ganglia 

 arise some days later. 



Some extirpation experiments were made on very young Amia 

 to determine, if possible, the mode of origin of the nervus te mi- 

 nalis. The nasal capsule was cut away from one side of the 

 young, one or two days after hatching. The object was to re- 

 move the olfactory capsule completely without too much injury 

 to adjacent parts. Probably complete removal was accomplished 

 in only two cases out of over twenty operations, for there were 

 some olfactory fibers found in all the nerves on which operations 

 were performed except two. The fishes on which operations 

 were made, were fixed and sectioned about a week or ten days 

 after the extirpations. It is impossible to state to what extent 

 regeneration of the olfactory nerve and placode took place in the 

 short time the operated fishes were permitted to live, but in 

 cases where one felt confident that all the placode was taken 

 away as a more or less adherent mass of cells, there were found 

 olfactory fibers later. It is probable that in all those cases where 

 olfactory fibers were found on sectioning, a few cells of the olfac- 

 tory placode were not removed in the operation. The number of 

 fibers varies from a very few to half as many as were found on the 

 uninjured side which was used for control. Along the fibers 



