cxxiv Journal of Comparative Neurology. 



guments for the existence of a third eye in Vertebrates. He combats es- 

 pecially the opinion expressed by Leydig that the cells of the pineal are 

 lymphatic vessels, and gives numerous proofs for the sensory character of 

 these cells. 



In spite of numerous researches, the histological structure, the func- 

 tion and the origin of the parietal organ is yet wrapped in mystery. 

 Most authors grant that it has at some time played the role of an eye. 

 Its optical characteristics however are greatly diminished in the actual 

 specimens. It is in direct relation with the epiphysis and is considered 

 by many as merely a differentiation of this organ. Leydig his raised 

 serious objections to considering it as an eye at all. He attributes lym- 

 phatic rather than sensory functions to the parietal organ. Does Leydig 

 sufficiently establish his position? I think not. The pineal eye is an 

 organ on the way to degeneration. It is not strange then that it has not 

 preserved the impress of its optic chiracteristics. The question is not 

 whether, in the retina of the third eye, ganglion cells and cones have been 

 found, but whether, taken as a whole, its characters ally it more with vs- 

 ual organs or not. 



Leydig argues that no nerve serves the parietal organ. If it has 

 served as a visual organ the nerve ought to remain. But no nerve b;ing 

 left proves that it never served the purpose of sight. He asserts that the 

 formation designated by Strahl, Martin, Francatte and others under the 

 name of parietal nerve, is either of a connective or vascular nature. 



Spencer finds in Saurians a nervous cord enclosing nuclei drawn out 

 and attached again to the pineal eye at the epiphysis. Leydig refuses to 

 see a nerve in the epiphysal cord of Spenser, but considers this formation 

 as terminating in the mesodermic lamina surrounding the pineal. In the 

 An^iiis fragilis I have discovered a slender bundle of fibrils starting from 

 the intermediate brain (diencephalon) in front of the base of the epiphysis 

 and endingin the retina of the parietal organ. I liken this bundle to a nerve, 

 but cannot yet trace it definitely to its point of origin. Strahl and Martin 

 and Francatte have asserted the existence of a pineal nerve independent of 

 th i epiphysis. The pineal eye is situated in the region of the plexus 

 choroideus and is often enveloped with a vascular net-work. One of thes-; 

 vessels, passing under the optic vesicle and penetrating between the 

 plexui choroid2us and the epiphysis, I have be;n able to follow exactly, 

 both in its origin and passage, and it is not to be confouad^d with a lym- 



