86 MORPHOLOGY OF THE ORGANS 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 eyes already 

 described in the relations of the nerves to 

 the retina (p. 81). 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 eye. 

 After the parietal eye 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 



FIG. 91. Dorsal view 

 of head of Sceleporus un- 

 dulatus; p, parietal organ. 



7 



FlG. 92. Pineal apparatus in an embryo lizard {Sceleporus}. b, blood-vessels; 

 c, cerebrum; e, epiphysis; />, parietal eye; pa, paraphysis; //, parapinealis. 



