148 FREDERICK TILNEY AND LUTHER F. WARREN 



The parietal or third eye does not make its appearance in 

 reptiles except in Sphenodon and Lacertilia vera. In these 

 latter forms it is by no means constant. Of forty-four species 

 examined, the parietal eye has been observed in 29 instances, 

 the retina in 28, the lens in 24, the parietal nerve in 25, the 

 cornea in 24, and the parietal foramen in 28. It was impossible 

 to detect these structures in the same number of species as 

 follows: Parietal eye absent in 9, retina absent in 11, lens absent 

 in 10, nerve absent in 12, cornea absent in 10, and parietal fora- 

 men absent in 10. The pineal organ, either complete in all its 

 three portions or as the proximal portion (epiphysis proper), 

 was present in all of the forty-four species. A complete pineal 

 organ was observed in thirty-one species while a highly devel- 

 oped proximal portion, possibly suggestive of glandular forma- 

 tion, was present in eight species. 



In Ophidia and Chelonia there was a total absence of the 

 parietal eye and structures pertaining thereto in all of the fifteen 

 species examined. In nine species of ophidians the pineal 

 organ was represented in nine instances by a definitely glandular 

 proximal portion, the epiphysis proper or corpus pineale. This 

 gland seems to contribute its secretion to the ventricles, but 

 may also be of the blood-vascular type as well. In Chelonia 

 there is evidence that the pineal organ which appears as the 

 proximal portion of that structure may also be glandular in 

 nature. The absence of the parietal eye elements as well as the 

 pineal organ has already been mentioned in Crocodilia. 



It is evident from this summary that only the proximal por- 

 tion of the pineal organ persists in the more modern reptiles, 

 while the parapineal element as well as the end-vesicle and stalk 

 of the pineal organ, have entirely disappeared. 



7. Comparative Anatomy and Histology of the Epiphyseal Complex 



in Birds 



As in ophidians, the only element of the epiphyseal complex 

 which persists in birds is the proximal portion of the pineal 

 organ. This presents itself as the epiphysis or corpus pineale. 



