Sorensen, Study of Epiphysis and Roof of Diencephalon. 59 



2. At the end of the 9th day there is still no trace of a 

 nerve to be seen entering the vesicle already separated from the 

 pineal. 



3. By the 14th day the nerve is formed and passes from 

 the floor of the eye-vesicle to a cell accumulation lying in the 

 roof of the diencephalon, called the parietal-centrum. 



4. The parietal-centrum lies asymmetrically to the right of 

 the middle line, immediately in front of the pineal evagination. 



5. In 24 to 27 days the nerve is surrounded by a connec- 

 tive tissue sheath (perineurium) and the parietal-centrum now 

 lies in a direct line with the right ganglion habenulae. 



6. In 35 to 40 days the nerve shows undoubted appear- 

 ances of degeneration that already appear to have produced 

 atrophy of its central part. 



7. In the adults the nervous elements are completely atro- 

 phied and only the thickened perineurium remains. 



8. In one embryo of Iguana there are two parietal nerves, 

 one from each ganglion habenulae. 



III. The Proximal Pineal. 



1. At the end of the 9th day the pineal in Iguana has the 

 form of a vesicle communicating with the third ventricle, which 

 shows a structure comparable to the parietal eye vesicle. 



2. In the course of development the pineal is covered with 

 cilia internally and is gradually transformed into a long funnel. 



3. The proximal part of the pineal retains a structure sug- 

 gestive of the medullary tube, while the distal part has a devel- 

 opment suggestive of the retina of the parietal eye. 



4. The coniform pineal of adult animals retains in its distal 

 end the funnel-shaped form as in embryos, while its proximal 

 part undergoes a follicular transformation through the growth of 

 the wall. 



5. The epiphysial evagination in Tejus shows in its early 

 embryology just as in Iguana, a constriction causing the division 

 into a distal part ( pineal-eye vesicle ) and a proximal part 

 (pineal). 



6. Later this constriction disappears again and the entire 

 primary epiphyial evagination is developed into a pineal. 



