MEDIAN EYES 



Pin At HC Mes 



717 



Fig. 863. — The Median Eye in the Ammoccete of the Lamprey, Petromyzon. 

 Longitudinal section through the roof of the fore- and mid-brain. AC, anterior 

 commissure ; At, atrium of the pineal organ ; HC, habenular commissure ; HG, 

 habenular ganglion ; HT, habenular tract ; Mes, mesencephalon ; Par, parietal 

 organ ; Pin, pineal organ ; PC, posterior commissure ; Pp, paraphysis (after 

 Studnicka). 



Fig. 86-4. — The Median Eye of Lampetra flvviatili^. 



Section through the head of the animal showing the two vesicular-like structures 

 in the centre of the figure, the pineal and i?arietal bodies, lying in the ventricle 

 underneath a relatively transparent area of skin and subcutaneous tissue. The two 

 solid masses in the lower portion of the picture represent parts of the brain (Mallory's 

 phospho-tungstic acid htematoxylin) ( X 24) (Katharine Tansley). 



1907-11 ; Nowikoff, 1910 ; Gasson, 1947 ; Trost, 1953). It is situated in the 

 parietal foramen of the cranial roof immediately under the integument and is covered 

 by a specially modified scale where the black pigment is absent and the green is only 

 feebly represented so that it is relatively transparent (Fig. 459). The eye takes the 

 form of a flattened vesicle lying in a connective tissue cajasule ; the cells of the distal 

 wall are elongated to form a lens which sometimes contains a central jDigmented area ; 

 the cells of the proximal wall are differentiated to form a retina (Fig. 865). In some 

 types such as the American " chameleon ", Anolis, the latter is relatively crude but 

 usually there is a reasonably well-differentiated sensory layer composed of visual and 



