86 MORPHOLOGY OF THE ORGAJ^S OF VERTEBRATES. 



differentiated, the former into a transparent lens-like body, the 

 latter into sense cells, supporting cells, and pigment cells, the 

 whole making up a retina. Thus is formed a camera eye ; and 

 in the lizards this comes to lie on the top 

 of the head just beneath the skin, one of 

 the plates of the dorsal surface bearing a 

 transparent spot through which light can 

 reach the organ. This parietal eye, how- 

 ever, differs from the paired e\es already 

 described in the relations of the ner\ es to 

 the retina (p. 8 1}. These proceed from the 

 deeper ends of the sense cells, but it must 

 be kept in mind that there has been no inver- 

 sion of the retinal layer in the parietal eve. 

 After the parietal e}e has been budded 

 off from the epiphysis, there is frequently 

 formed a less perfect eye-like organ, the 

 parapinealiS; from the distal end of the stalk. In some cases 

 the epiphysis is double, in which case the pinealis arises 



•^J^v=«^^lv 



Fig. 91. Dorsal view 

 of head of Sccid/ontj un- 

 dulatus; p, parietal organ. 



Fig. 92. Pineal apparatus in an embr)-o lizard ( S.-d.-foms). b, blood-vessels ; 

 c, cerebrum; e, epiphysis; /, parietal ey^; pa, paraphysis; //, parapinealis. 



