NERVUS TERMINALIS IN AMIA 5/ 



teus with the sucking disk or adhesive gland on the snout of the 

 young which has been described by Dean ('97) and others; but 

 on examination it was found that the sucking disk had already 

 atrophied to a large extent before the ganglion can be recognized 

 in the young. 



In the description that follows, I shall employ the term nervus 

 terminalis which has been largely used in the literature recently, 

 although it will appear that I do not have any evidence that the 

 nerve is separate from the olfactory nerve in the fishes which I 

 have examined, and consequently I am led to the view that it is 

 a part or component of the olfactory nerve, as Locy ('99) in his 

 first work on its development in the sharks considered it. 



EMBRYOLOGICAL DEVELOPMENT OF THE OLFACTORY ORGAN 



IX AMIA 



The sections on which my study of the early embryology of 

 the nasal pit is based were cut transversely or horizontally six 

 micra thick and stained with iron hematoxylin and acidfuchsin. 

 The series of embryos first described were all taken from a single 

 nest from May 17 to May 20, 1908, and fixed in Zenker's fluid 

 at intervals of three hours. Only such stages will be described 

 as show differences worthy of note as compared with earlier 

 stages. 



At a period forty hours before hatching and consequently 

 about eighty hours after fertilization, since it takes Amia eggs 

 about five days to hatch, the nasal placodes are quite readily 

 recognizable as solid masses of cells occupying much of the space 

 between the optic cups posteriorly and the sucking disk anteriorly 

 and ventrally. They are somewhat pearshaped with the smaller 

 end pointing forward and downward between the two developing 

 halves of the sucking disk with which they come into contact. 

 At this stage the olfactory cups meet each other at their anterior 

 ends in a common mass of cells (fig. 1) situated ventrally between 

 the two developing halves of the sucking disk. The plane of the 

 section figured slants upward and backward. There is between 

 this unpaired portion of the olfactory placode, which is not far 



