40 



FREDERICK TILNEY AND LUTHER F. WARREN 



end-vesicle, a stalk and a proximal portion connecting it with a 

 ventricle of the brain. At first, the end-vesicle contains a cavity 

 which gradually decreases in size so that the lumen becomes 

 little more than a cleft or entirely disappears. The stalk also 

 contains a large canal which is gradually reduced in size. The 

 ventral wall of the end-sac becomes converted into a structure 

 resembling the retina, in which many nerve fibers are to be 

 observed. In the dorsal wall of the sac nerve fibers running 

 from the end-vesicle soon make their appearance. These fibers 

 come into relation with the posterior commissure and constitute 

 what is known as the nervus pinealis. The proximal portion is 

 represented by a very short, dilated structure which contains 

 the recessus pinealis. 



Fig. 9 Anlage of the epiphyseal conplex in an embryo of Petromyzon, accord- 

 ing to Kupffer, 1904. 



Ls., lamina terminalis; Pp., paraphysis; Ch., commissura habenularis; Po., 

 pineal organ; Cp., commissura posterior. 



At a considerably later embryonic period the anlage of Stud- 

 nicka's parapineal organ first makes its appearance. It develops 

 entirely independent of the anlage of the pineal organ. The 

 evagination which first makes its appearance as the parapineal 

 anlage shortly becomes greatly elongated to form a tubular 

 prolongation from the roof of the brain. The terminal portion of 

 this tubular evagination becomes dilated to form, as in the case of 

 the pineal organ, an end- vesicle, while a slender stalk connects the 

 latter with the brain roof. The ventral wall of the end-sac of 

 the parapineal organ, as in the case of the pineal organ, develops 



