PINEAL EYE OF YOUNG AND ADULT AWGUIS FRAGILIS. 98 
of quite secondary signification. For the image which it 
perceives from the outer world must be quite a dim one as 
compared with that of the paired eye; firstly, because its 
retina is not at all so highly differentiated as in the paired 
eye; secondly, because some parts of the retina are quite 
shut up by the overlying pigment; thirdly, because the 
connective tissue which lies on the top of the lens is by no 
means so clear and transparent as the cornea of the paired 
eye. So the pineal eye would be of very little use in 
suarding against enemies, and as for looking for food, an 
eye on the top of the head cannot be of any use whatever. 
And these two functions, searching for food and guarding 
against enemies, are the most important which the eyes of 
a blindworm have to perform. Besides this, the paired eyes 
of Anguis being placed on the sides of the head, may be 
able to see a good deal of what is going on above the head 
of the animal. Thus we find that an imperfect seeing 
organ on the dorsal surface of the head of Anguwis would be 
of very little or no use to the animal. 
Tt is much more probable, I think, that the pineal eye is 
an organ for feeling temperature, and certainly its structure 
seems perfectly suitable for that purpose. Rays of light 
can easily penetrate down to the pigmented layer, for in 
the living animal we can see the pigment layer shining 
through the skin. Rays of heat, of course, as being 
essentially the same as rays of light, could easily penetrate 
the ectoderm and the thin layer of connective tissue, and 
then they would be concentrated by the lens and thrown 
upon the pigmented layer. Here they would be absorbed 
and their action transferred by the “‘ retina,” the stalk of 
the eye and the epiphysis proper to the brain, to produce 
there the sensation of heat. 
Therefore, if the facts which I have brought forward, 
and the conclusions drawn from them, are right, then we 
