214 THE PINEAL ORGAN 



the left of the posterior organ. Its distal end is directed forward and 

 encloses a small cavity which communicates with the ventricle. In 15-mm. 

 embryos this communication is found to be closed ; anteriorly it ends in a 

 solid ovoid mass of cells which shows only a trace of a lumen. According 

 to Eycleshymer (Figs. 149 and 150) a lumen appears first in 5 to 6-mm. 

 embryos. He also describes nerve-fibres which, coming from the 

 habenular commissure, penetrate the substance of the anterior organ ; 



a B 



c Ac pn Ac.pn^D 



Pn ^4 



Fig. 



150. 

 from Serial 

 Davis.) 



Drawings of Models of the Epiphyses of Amia, Reconstructed 



Sections ; seen from Above. (After Eycleshymer and 



A — Larva 6-7 days old ; 4-5 mm. ; 100. 

 B — Larva 9 days old ; 6-7 mm. ; 100. 

 C — Larva 10 days old.; 7-8 mm. ; 100. 

 D — Larva 14-15 days old; 9-10 mm. ; 100. 



Ac. pn. : accessory epiphysis, or left pineal organ. 



Ca. : caudal end. Pn. : pineal organ (Epiphysis 



Ce. : cephalic end. posterior epiphysis). 



/. : left side. r. : right side. 



st. : stalk. 



II or 



and, in an earlier stage — 12 to 13 -mm. embryos — similar nerve-fibres 

 which enter the posterior organ (Fig. 149, F). Later the anterior organ 

 was found by Hill to have disappeared ; but Kingsbury has described 

 an adult specimen of Amia calva (Fig. 151) in which the left pineal organ 

 was still present although less developed than the right organ. It consisted 

 of a hollow vesicle which was connected by a thick nerve-cord with the 

 left habenular ganglion. The left habenular ganglion, in correspondence 

 with the small size of the left pineal organ as compared with the right 

 pineal organ, was smaller than the right habenular ganglion (Fig. 151). 

 The two organs were enclosed in a membranous septum formed by two 

 opposed layers of the dorsal sac. This sac is very large in Amia, and is 

 prolonged backwards in the pineal region where in the section shown 

 in the figure, four posterior diverticula have been cut across. From the 



