PINEAL EYE IN LAOERTILIA. 205 



As described by de Graaf, the eye is separated off from the 

 epiphysis. In his figure the lens is shown completely separated 

 off from the retina, which overlaps it anteriorly. This does 

 not appear to be the case ; but, on the contrary, the eye, as 

 far as could be told, agreed with all other forms examined in 

 having the lens directly continuous with the posterior walls of 

 the vesicle.^ 



The most important point of difference, however, is concerned 

 with the retina. De Graaf figures this (PL 4, fig. 34) as 

 having a layer of unpigmented rods (si.) — his " Staafjeslaag^^ — 

 together with a layer of unpigmented cells (cep.) — his " Cyilin- 

 dercellenlaag" — lying internal to the pigmented rods. 

 Of neither of these two layers can I succeed in finding any 

 trace, either in Anguis fragilis, or in any of the forms yet 

 examined. In every instance all that can be discerned within 

 the rods is merely the remains of what may be supposed to have 

 been during life the fluid contents of the vesicle. In coagu- 

 lating this does in some instances appear to attach itself to the 

 parts of the rods facing into the cavity, but never forms, in any 

 specimen examined hitherto, any structures so definite as to be 

 interpreted into the " Staafjeslaag" or "Cyllindercellenlaag" 

 of de Graaf. 



Cyclodus gigas, PI. XV, fig. 9; PI. XVI, figs. 18, 19, and 

 20 ; PI. XVIII, fig. 29 ; PL XX, fig. 5. 



In Cyclodus the epiphysis is not developed into an eye, 

 but the structure is nevertheless in an interesting state, showing 

 most probably a stage passed through during the development 

 of the eye in other forms. 



External Appearance. — In fig. 9 is represented a portion 

 of the scale specially modified in connection with the organ. 

 It lies, as in all other forms, in the median line posterior to 



' In my first communication to ' Nature/ the leus of Hatteria was described 

 as separated from tlie retina, but examination of a fresli specimen showed at 

 once this was a result due to slight post-mortem degeneration of the tissues, 

 and that in reality the two were perfectly continuous, a result which subse- 

 quent investigations of many forms has fully confirmed. 



