PlNBAL BYE IN LAOERTILIA. 195 



Plica (Uraniscodon) umbra. 



In this the external indication is particularly clear. The 

 scales on the dorsal surface of the head are small, save one 

 whose great size renders it prominent ; in the centre of this a 

 small, white, slightly dome-shaped structure indicates the 

 position of the eye beneath. 



Position of the eye. — The organ lies very far forward on 

 the dorsal surface, being placed (PI. XIX, fig. 35) over the 

 anterior region of the cerebral hemispheres; it is situated 

 within the parietal foramen, the size of which is far greater 

 than that of the eye itself, which lies embedded in connective 

 tissue. The usual absence of pigment immediately above it is 

 to be noted. 



Structure. — The organ was not in a good enough state of 

 preservation histologically to render any detailed examination 

 of its structure possible. So far as could be discerned the con- 

 nection of the eye with the epiphysis is retained_, the solid pineal 

 stalk {Op. s.) running backward immediately within the skull 

 cavity. Attention may be drawn to one curious point — close 

 to the eye is a small secondary and deeply pigmented vesicle 

 (op^.). It may be possible that in the specimen examined this 

 is merely due to a shrinkage of the walls of the whole optic 

 vesicle, whereby the anterior and posterior have come into close 

 contact, and thus simulated the appearance of two vesicles, but 

 as far as could be ascertained, this was not the case. The deep 

 pigmentation of the anterior as well as the posterior wall is 

 strong evidence against this view. 



Iguana tuberculata, PI. XV, figs. 15 and 16; PI. XXVIl, 



fig. 23. 



The full description of the organ, which is present highly 

 developed in Iguana is not given in this paper. I hope before 

 long to have the opportunity of examining its structure in a 

 living specimen. 



External Indication. — The usual modified scale is present 

 and in large specimens is very conspicuous. In smaller ones 

 (PI. XV, fig. 16) a slightly raised central portion is present. 



