30o 



SCIENCE PROGRESS 



posterior, so that the pineal or parietal "eye," developed from 

 the former, may perhaps after all be regarded as a portion of 

 the epiphysis constricted off from the remainder, which forms 

 the "stalk." This author also states that in Iguana the "stalk," 

 after giving off the "parietal eye," may, by constriction of its 

 apex, give rise to a second pigmented vesicle, which he 

 distinguishes as the "Zirbel-Auge." 



Some light is thrown upon this difficult problem by the 

 investigation of the pineal organs and their development in 

 the remarkable reptile Sphenodon (Hatteria), the sole surviving 





A 



B 



M-- ' 



FlG. 4. — A, B, c. Three stages in the development of the pineal organs of the tuatara 

 (Sphenodon), as seen in longitudinal vertical sections of young embryos. (The 

 anterior end is towards the left side of the diagram in each case.) 



C.P., Posterior commissure ; Ep. 1, anterior (left) epiphysial outgrowth (pineal eye) ; Ep. 2, 

 posterior epiphysial outgrowth (pineal stalk); Le., "lens" of pineal eye; Ret., retina of 

 pineal eye. 



representative of the very ancient group Rhynchocephala, and 

 now confined to certain small islands off the coast of New 

 Zealand, where it is known under the native name of " tuatara." 

 This investigation I was fortunately able to carry out myself 

 while in New Zealand, and the results were published in 

 The Quarterly Journal of Microscopical Science in 1899. The 

 earliest indication of the pineal organs in Sphenodon is in 

 the form of a small vesicular outgrowth of the roof of the 



