Eycleshymer-Davis, Epiphysis and Paraphysis in Amia. 57 



comes thickened in the earher stages but later undergoes but 

 little change. The cells lining both stalk and vesicle become 

 ovate-lanceolate in the 12-16 mm. stages, and are arranged so 

 that their pointed ends are directed inward. The lumen of both 

 stalk and vesicle are at this time filled with a coagulum. In 

 the \2 mm. stage we have found nerve fibres passing from the 

 superior commissure into the stalk of the primary vesicle. In 

 the stages between 6 and 12 mm. the position of the vesicle is 

 externally visible owing to the retarded formation of pigment 

 in this area. Another point of interest is the thinning of the 

 cartilage just above the primary vesicle. The primary vesicle 

 as it enlarges grows forward, the angle formed with the hori- 

 zontal plane is at first about 5°- 10°, while in its final position it 

 forms an angle of 45°-6o°. 



The secondary vesicle does not form until long after the 

 primary. It usually appears on the 7th or 8th day, yet in some 

 cases it does not appear until the 9th day. Its beginning is a 

 slight thickening in the anterior portion of the dorsal wall of 

 the primary vesicle; this thickening is in the median line and is 

 accompanied by a slight evagination of the wall of the primary 

 vesicle. As the secondary enlarges it shifts its position to the 

 left until the two vesicles lie side by side. It is interesting to 

 note that this vesicle in a number of cases lies on the opposite 

 side of the primary. A well defined cavity is present in the 

 15 mm. stage yet in no case have we found it well defined in 

 the earlier stages. At this time it lies practically free from the 

 primary. In one instance we have traced nerve fibres from the 

 superior commissure into the basal portion of this vesicle. 

 From the 15 mm. stage on this vesicle becomes smaller, loses 

 its cavity and undergoes other changes which are probably in- 

 dicative of degeneration. It may ultimately disappear. This 

 must be determined by studying stages beyond the 30 mm. 

 larvae. 



The paraphysis arises later than the secondary epiphysis. 

 Its beginning is usually foretold by a thickened area of the epi- 

 thelium forming the roof of the prosencephalon which soon gives 

 rise to a posteriorly directed evagination. The structure in- 



