RlTTER, — Parietal Eve 



ABBREVIATIONS. 



cav e'phy. Cavity of the epiphysis. 



cbl. Cerebellum. 



ceb. Cerebrum. 



(/is. opt. Optic chiasm. 



'/. /. Cells of zone 5 of the retina. 



cl. Ins. Cells of the lens. 



cog. Coagulum. 



com. a. Anterior commissure. 



com. p. Posterior commissure. 



com. su. Superior commissure. 



con't. tis. Connective tissue. 



cp. sng. Blood corpuscles. 



e'drm. Ectoderm. 



en'th. va. Endothelium of retinal blood- 

 vessels. 



ep/i- vs. Epithelium of the epiphysial 

 vesicle. 



e'th. Epithelium. 



la. trm. Lamina terminalis. 



Ins. Lens. 



lob. opt. Optic lobes. 



m. scu. Scale of the parietal eye. 



* Processes secreted from 



rtn. 



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. 



the inner surface of the 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 Stansbunana. Diagrammatic in unimportant details. X 312. 



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

 Stansbunana. X 8. 





