THE PINEAL GLAND 287 



the parietal organ, to which he gave the name " Leydig's body," 

 was a portion of the epiphysis constricted off from the remainder. 

 Again in 1884 Ahlborn came to the conclusion that the epiphysis 

 or pineal gland is the vestige of an unpaired eye, analogous to 

 the unpaired eye of tunicates and perhaps also of Amphioxas, 

 basing his conclusions mainly on his own classical researches 

 on the brain of the lamprey. 



So far, however, the evidence in favour of the visual character 

 of the parietal or pineal sense-organ had been but slight, and it 

 was not until 1886 that this view received much support. In 

 that year H. W. de Graaf published a short paper in the 

 Zoologischer Anzeiger on the Anatomy and Development of 

 the Epiphysis in Amphibia and Reptiles. In this paper the 

 author maintains that whereas in the Anura the extremity of 

 the epiphysis becomes constricted off to form the "gland of 

 Stieda" or "Stirndriise," lying outside the cranium in the middle 

 of the dorsal surface of the head, and exhibits no eye-like 

 character, in Lacerta and Angitis, on the other hand, the same 

 organ acquires a distinctly eye-like structure comparable to that 

 of the eyes of certain invertebrates. He further calls attention 

 to the parietal foramen in the extinct labyrinthodonts of the 

 Carboniferous, Permian, and Triassic epochs, and concludes 

 that the epiphysis in the ancestors of living animals must have 

 played a very important part as a sense-organ. This paper, 

 although only of the nature of a preliminary communication, 

 contains a striking figure of the pineal or parietal " eye " in 

 Anguis fragilis, to which no doubt was due in large measure 

 the interest which it excited. The author's complete memoir, 

 with a still more beautiful figure of the organ in question, was 

 published in the same year. In the meantime the matter had 

 been taken up in England by Baldwin Spencer, who, while 

 giving full credit to de Graaf for his work, greatly extended 

 our knowledge of the subject by the investigation of numerous 

 lacertilian types and of the remarkable reptile Sphenodon 

 (Hatteria), in which the " pineal eye" still exhibits a very high 

 degree of organisation. Spencer's beautifully illustrated memoir 

 (published in The Quarterly Journal of Microscopical Science for 

 October 1886) naturally served to greatly intensify the interest 

 which had already been aroused on this subject, and from this time 

 onwards the literature dealing with the pineal apparatus and the 

 parts of the brain associated therewith increased rapidly. 



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