THE PINEAL GLAND. 



127 



covering that in tlie slow-worm the pineal gland is 

 actually modified into a structure resembling an inver- 

 tebrate eye. This remarkable structure has since been 

 examined in various Eeptilia by Mr. Spencer.* It 

 appears to be more highly organized in Hatteria than 

 in any other form yet studied ; but the retrogression of 

 the different structures has not proceeded j^ari passu, 

 in some cases the lens, in some the retina, in others 

 the nerve, having been most modified, or having dis- 

 appeared. In Hatteria and Varanus the eye is very 

 distinct ; the interior parts being more perfect in the 

 former ; while in the latter it is externally most con- 

 spicuous, standing out prominently from its creamy 

 whiteness. The lens is cellular in structure, and thins 

 away rapidly at the sides. The " rods " are well 

 developed, and embedded in pigment. 



Spencer describes the various modifications of the 

 organ in the iguanas, chame- 

 leons, flying lizards, geckos, etc. 

 , Fig. 81 represents the ex- 

 ternal aspects of the eye-scale 

 in a small lizard (Calotis), with 

 the transparent cornea in the 

 middle, through which the eye 

 is seen ; and the diagram 

 Fig. 82 a section through 

 the eye-scale of a small lizard 

 (Lacerta). 



A very interesting point in 

 connection with the pineal eye 

 consists in the fact that the optic nerve does not 

 penetrate the retina, and then spread out on its outer 



* Quarterly Journal of Microscopical Science, October, 1886. 



Fig. 81.— Pineal eye-scale on the 

 head of a small lizard (Calotis) ; 

 after Spencer. 



