THE PINEAL BODY 



99 



method described the structure in Acipenser rubicundus. Both 

 observers were able to differentiate a saccular proximal portion 

 resembling the recessus pinealis, a thin, dorsoventrally extend- 

 ing stalk, the latter producing a groove in the dorsal surface 

 of the dorsal sac, and finally an end-vesicle greatly dilated. 

 The end-vesicle was of considerable size and contained a well- 

 marked cavity. 



Its walls showed no tendency to differentiation into a dorsal 

 pellucidal layer or a ventral retinal layer. According to Stud- 

 nicka, 386 the entire end- vesicle consists of rather long cylindrical 



Hm 



Opt 



Fig. 51 The pineal region in Polyodon folium, according to Garman, 1896. 

 Olf., olfactory lobe; Opt., optic nerve; Hm., hemisphere; Po., pineal organ; 

 St., stalk. 



cells with a generally oval nucleus and two processes, one a 

 slender extension reaching in toward the lumen of the pineal 

 organ and the other a more diffuse ending, extending toward 

 the ectal surface of the wall. Scattered here and there among 

 these cells, which are in the majority, are a number of large 

 elements more distinctly oval in character with a rounded 

 nucleus situated near the center. Some smaller elements are 

 also found scattered more numerously among both types of 

 cells. Studnicka describes them, first, as ependymal cells; 

 second, as sense cells, a larger-sized cell which he thinks may 



