244 



THE PINEAL ORGAN 



(8) The parietal eye is phylogenetically bilateral. In ontogeny, 

 indications of this condition are present in reptiles, e.g. Sphetiodon, 

 and also in other classes of vertebrates, e.g. Geotria. Thus in Sphenodon 



Fig. 173. — Longitudinal Vertical Section through Pineal Organ of Lacerta 

 muralis (25 mm.) showing terminal vesicle. (nowikoff.) 



d.s. : dorsal sac. p.e. : parietal eye. 



h.c. : habenular or anterior commissure. p.n. : parietal nerve. 



par. : paraphysis. p. st. : pineal stalk. 



p.c. : posterior commissure. p.s. : pineal sac. 



Fig. 174. — The End Vesicle and the Distal Part of the Stalk of the Pineal 

 Organ,and a Part of the Parietal Eye of Pseudopus Pallasii. (After 

 Studnicka.) 



ace. : accessory pineal organ. pin. : end vesicle of pineal organ. 



bl. : blood-vessel. r. sk. : roof of skull. 



par. f. : parietal foramen. st. : stalk. 



par. 0. : part of the parietal organ. 



