i66 THE POPULAR SCIENCE MONTHLY. 



dermis, set on the extremity of a pineal outgrowth from the 

 brain. The clear area around it is caused by the dermis, which is 

 transparent and free from the pigment which covers it internally 

 in other parts. The eye is covered by an escutcheon-shaped epi- 

 dermal shield, more transparent in the center and larger (three 

 by three millimetres) than the normal epidermal scales. The only 

 sign of degeneracy is the central cloudy mass of pigment, like a 

 big cataract." 



I was naturally desirous of determining for myself how far it 

 was sensitive to light, but found the investigation beset with dif- 

 ficulties. Chloroformed lizards that were deprived of their eyes, 

 although the amputation was dexterously performed, did not 

 revive sufficiently to make their subsequent movements suggest- 

 ive ; or did sympathetic ophthalmia set in and affect the pineal 

 eye ? 



I subsequently hit upon a plan, using very thin India-rubber 

 cloth, by which the eyes proper were effectually closed, and the 

 " eye " of the vertex left free. The lizards thus provided with a 

 blinding head-gear were separated from their fellows and placed 

 in a roomy inclosure, made up of several almost dark and very 

 light alternate sections, the temperature being even throughout 

 the lizards' range. The arrangement was, perhaps, too artificial 

 for a satisfactory series of observations, but it became evident at 

 once that the lizards recognized the difference between the dark 

 and light areas, and their prompt return to the latter when re- 

 moved from them, and again their actions when they returned, 

 all showed the appreciation of a difference, which I know was not 

 one of temperature, but beyond this I could determine nothing ; 

 but I recalled, at this juncture, the significant fact that in the 

 woods about May's Landing I noticed many lizards buried in the 

 fine sand and leaf -mold, their eyes closed and covered, but the 

 top of the head and a portion of the back, for its whole length, 

 exposed. The same was subsequently noted as a position fre- 

 quently assumed by the lizards in my Wardian cases. If, there- 

 fore, the " pineal eye " is sensitive to light, it is still of some use 

 to the creature, as it would certainly respond to a passing shadow, 

 and so warn the animal of the approach of a possible enemy. It 

 certainly would be greatly to the lizard's advantage if it had a 

 perfect eye in the top of its head, especially when it rests upon 

 the trunks of trees, and is exposed to the attacks of predatory 

 birds ; but the " pineal eye " is at most but a remote approach to 

 this. On the other hand, it was found that whenever I converged 

 the rays of light with a burning-glass, always so suddenly that 

 no thermal effect was produced, there was caused a movement of 

 uneasiness, a flinching, on the part of the lizard that was ex- 

 tremely suggestive. 



