THE PINEAL GLAND. 



127 



covering tliat iu the slow-worm the pmeal 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 pari passu, 

 iu some cases the lens, la 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 

 whit^ess. 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 (Oalotis), with 

 the transparent cornea in the 

 middle, through which the eye 

 is seen; and the diagram 

 Pig. 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 tlie 

 head of a small lizard (Calotis) ; 

 after Spencer. 



