100 



FREDERICK TILXKY AXI) LTTHKU 1. WAHHKX 



lie li'an^lionic cells, and, third, iieuroo-lia cells which arc smaller 

 ;'iid vnerally more deeply situated elements in the walls of the 

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



a b 



Fig. 52 a, Pineal organ in Acipcnscr nil>irun<lus. l>, 1'inral organ in Polyo- 



d<ui foliiirn. 



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

 h-nirtl, from the roof-plate end-\'(>sicle. Its walls are made up 

 of small neuroglia c< i lls, whil(> in the mon* dorsal of the two walls 



