60 CHARLES W. HARGITT 



however, that the pigment patterns on the legs, and especially 

 the dorsum, afford a fairly good basis. It seems quite as decisive 

 as that of the lateral spines of the lizard, Phrynosoma, which 

 Parker ('06) employed in his experiments. I regret not to 

 have secured successful photographs of extremes in either direc- 

 tion; such figures are, however, admirably shown in " The Frog 

 Book," PL XLVI. 



As to the chemistry or mechanics of color change I shall not 

 attempt a formal discussion or explanation. Those who are 

 concerned with this feature may find extended details in the paper 

 of Biedermann ('92), or in the paper of Parker (op. cit.). It 

 may suffice here to merely say that skin color is due to the 

 presence in the derma of certain pigment granules, usually 

 contained in large pigment cells known as chromatophores, 

 melanophores, etc. These granules are capable of migration dis- 

 tally, that is, toward the surface, or in the opposite direction, under 

 certain stimuli. Certain other cells of the epidermis or sub- 

 epidermis, known as guanin cells, form a reflecting layer which, 

 on the contraction of the chromatophores act as a screen to 

 obscure the pigment and at the same time reflect from their 

 surface light falling upon it from outside. In a word, then, the 

 distal migration of the chromatophores accentuates the appro- 

 priate color, while the migration in the opposite, or proximal 

 direction decreases the color elements, and the guanin layer 

 reflects the lighter color of its own cells. 



In the laboratory the first attempt was to test the effects 

 of light in relation to color. In the first series of tests five speci- 

 mens were used, which were placed in glass jars of about two 

 or three gallons capacity, perhaps nine inches in diameter by 

 15 inches high. Into one of these damp moss was placed, and 

 in the other a branch with lateral twigs, and the tops closed by 

 wire screens. These cages were at first kept in my private labora- 

 tory where a fairly uniform temperature was maintained, and 

 w T here was a, good diffused light from north windows. For 

 experiments with direct sunlight the specimens were carried 

 into an adjacent laboratory having east windows. The first 

 experiments were simply the transfer of a cage from a remote 

 and darker part of the room to a table close to the window, or 

 even upon the ledge of the window. My records show a general 

 lightening of the skin color as a result; but as will be seen later 



