RiTTER. — Parietal Eye 



ABBREVIATIONS. 



Spot marking the position 

 of the parietal organ. 



External basement mem- 

 brane, [brane. 



Internal basement mem- 

 Nucleus. 



Nuclei of zone 2 of retina. 



Nuclei of zone 4 of retina. 



Nuclei of zone 5 of retina. 



Parietal bone. 



Pigment. 



Processes radiating from the 

 external basement mem- 

 brane. 



Retina. 



Blood sinus. 



Roof of the optic thalamus. 



Optic thalamus. 



Retinal blood-vessels. 



Third ventricle of brain. 



Epiphysial vesicle. 



Second zone of retina. 



PLATE II. 



Fig. 5. A portion of a section near the median plane, through the same eye as 

 that represented in Figure 1, more highly magnified. X 570. 



" 6. Sagittal section of the dorsal wall of the head, with the parietal organ 

 of Uta Stansburiana. Diagrammatic in unimportant details. X 012. 



" 7. External view of the parietal eye and surrounding structures in Uia 

 Stansbunana. X 8. 



