70 CHARLES BROOKOVER 



were found sheath cells and a small ganglion of the nervus termi- 

 nalis somewhat proportional to the size of the olfactory nerve 

 as compared with the ganglion and olfactory nerve on the unin- 

 jured side. 



Taking the inhalent nasal tube as a landmark, in some cases 

 it appeared that more of the posterior part of the nasal placode 

 had been removed and in other cases the anterior part. However, 

 it did not seem to make any appreciable difference in the develop- 

 ment of the ganglion whether the anterior or the posterior part 

 of the nasal capsule was removed. From this fact we may 

 infer that the ganglion of the nervus terminalis does not originate 

 from any particular part of the olfactory placode. In the two 

 cases where there were no olfactory fibers, no ganglion appeared, 

 although small blood vessels were found near the brain and it is 

 to be noted that the ganglion always appears near the blood 

 vessels (fig. 7). From these experiments it appears, also, that the 

 ganglion does not regenerate from the brain. The extirpation 

 experiments taken by themselves do not absolutely prove that 

 the ganglion does not arise from some other source near the 

 olfactory placode, which source was disturbed in the operations 

 that destroyed the placodes but, taken in conjunction with the 

 embryological history of the ganglion previously given, they 

 contribute some evidence to show that the ganglion is derived 

 from the olfactory placode. 



We may briefly sum up the early embryological history of the 

 peripheral olfactory apparatus in Amia by saying that at a time 

 about forty hours before hatching, two olfactory placodes exist 

 in connection with what may be termed an unpaired olfactory 

 placode. The latter disappears and the paired placodes imme- 

 diately establish fibrous connection with the neural tube. Later, 

 nuclei migrate out from the nasal sacs along the olfactory fibers 

 as Disse ('96), and others have found for other forms of verte- 

 brates. Still later some of the nuclei which have wandered out 

 along the nerve form a ganglion, as Carpenter ('00) found for 

 the ciliary ganglion in the chick, while others remain scattered 

 among the olfactory fibers as sheath cells. In case of the ciliary 

 ganglion, however, the nuclei migrate from the neural tube 



