100 FREDERICK TILNEY AND LUTHER F. WARREN 



be ganglionic cells, and, third, neuroglia cells which are smaller 

 and generally more deeply situated elements in the walls of the 

 end-vesicle. The stalk is strand-like in appearance and may 



* b 



Fig. 52 a, Pineal organ in Acipenser rubicundus. b, Pineal organ in Polyo- 

 don folium. 



contain a lumen in part of its extent or else running the entire 

 length from the roof-plate end-vesicle. Its walls are made up 

 of small neuroglia cells, while in the more dorsal of the two walls 



