PINEAL EYE IN LAOBRTILIA. 217 



viously described by myself, a most noticeable feature is the 

 absence of pigment between the eye and the exterior. This is 

 certainly very clearly marked and, further, is perfectly constant; 

 but there can be no doubt, in face of the descriptions given 

 above, that, if we use the term " rudimentary organs " to 

 include such as are now from change in their structure less 

 capable of fulfilling their function than they have been at 

 some previous time, then within this category must certainly 

 be included the pineal eye of Lacertilia. Such features as the 

 great development of pigment in, for example. Varan us, or 

 the loss of connection with the brain in many, such as 

 Calotes, are surely only capable of explanation on the suppo- 

 sition that the organ is rudimentary. 



One of the most prominent features in connection with the 

 organ is its Invertebrate structure. This was pointed 

 out by de Graaf in Angius fragilis, but in none of the 

 forms examined have any structures equivalent to the rod-like 

 bodies placed internally to those embedded in deep pigment, 

 described and figured by him as present in the above-men- 

 tioned species, been found. There is often, however, a struc- 

 tureless substance resembling a coagulum present within the 

 vesicle, which doubtless represents the remains of a humour 

 which was fluid during life ; in certain cases it appears to have 

 attached itself to the inner ends of the rods and thus simulates 

 to a certain extent elements lying internal to and connected 

 with them. Further, there seems to be but little ground for 

 likening the eye to that of Cephalopods and Pteropods, as is 

 done by de Graaf; the structure of the retina is different, and 

 that of the lens essentially so, being formed as a cuticular se- 

 cretion in Mollusca, whilst in Lacertilia it is distinctly cellular 

 and formed directly from the cells of the neural canal. 



As before ^ pointed out the development and structure ot 

 this organ is extremely interesting, as showing that out of 

 the walls of a vesicle originating as a hollow out- 

 growth from the neural canal, may be formed an optic 

 ' ' Nature,' May, 1886. 



