56 



FREDERICK TILNEY AND LUTHER F. WARREN 



however, is the more important of the two in amphibia, Cam- 

 eron believes that there is evidence of a bilateral origin to be 

 found in the later stages of amphibian development. The 

 portion of the anlage in connection with the superior commissure 

 corresponds to the parietal eye of Sphenodon while the remainder 

 corresponds to the epiphyseal stalk. From this evidence in 

 amphibia he is inclined to agree with Dendy 86 that the ancestors 

 of vertebrates must have possessed a pair of parietal eyes (figs. 

 22 and 23). 





Fig. 21 Anlage of the epiphyseal complex in an embryo of Triton cristatus, 

 according to deGraaf, 1886. 



Ch., commissura habenularis; R., recessus and pineal organ; Cp., commissura 

 posterior; M., midbrain; Epid., epidermis; Cor., corium. 



6. The development of the epiphyseal complex in reptilia 



The fact that in Prosaurians and Saurians a well developed 

 eye is found in many forms has been the cause of much dis- 

 cussion as to the embryolgical process by means of which this 

 structure is differentiated from the epiphyseal complex. Accord- 

 ing to the older view, the parietal eye arose, as in the case of the 

 isolated end-vesicle of amphibia, by a process of constriction 

 from the terminal portion of the pineal organ. Subsequently 

 the view was advanced that instead of a process of constriction 



