COLOURATiON OF REPTILES AND AMrJilBlANS. 269 



" protective colouration.'' The median and lateral stripes so 

 harmonize with the grass that often I have watched a specimen 

 disappear in a tuft, but failed to find it again. The long slender 

 body helps to give effect to the stripes ; one sometimes catches a 

 ghmpse of the white under-surface, and the beast is gone as 

 completely as if it sank into the earth. It should be mentioned 

 that this snake is very swift, and its colouration is permanent. 



Experiments Bp:aring on the Colour Meciianls^e in 

 Reptiles and Amphibians. 



The following simple experiments were performed in the 

 hope of obtaining some data relating to the colour mechamsm: 

 some of them, unfortunately, are inconclusive. 



I put an adult male A. aculeata, of a dark brown ground 

 colour dotted here and there with darker patches, into a fairly 

 small tin box, the lid of which was close-fitting and overlapped 

 the sides, so that light was entirely eliminated- This I exposed 

 to the direct rays of the sun, and in 35 minutes the colour had 

 changed to a cream ground with light brown patches and lighter 

 vermiculations ; the scales on the sides of the head green. 1 then 

 removed him to an ice-chest, and in ten minutes he Avas a uniform 

 reddish brown, with variously coloured scales on the vertebral 

 line. In five minutes more he seemed quite paralysed and in a 

 torpid state ! The vertebral crest was erected about a quarter 

 of an inch when the creature was first exposed to the heat, and 

 remained so even in the ice-chest. Agama atra, when suljjected 

 to the same drastic treatment, acted in a similar way, becoming 

 light when exposed to great heat and dark when subjected to 

 cold.* The blue, however, of the ventral side did not change. 



It is doubtful if these changes were entirely due to tem- 

 perature, for when the heat became intense in the box the lizard 

 always struggled to get out ; hence there may have been a certain 

 amount of nervous excitement. Certainly there was no ques- 

 tion of light; the lid was so tight-fitting that I doubt if a |)hoto- 

 graphic plate, inserted for the same period and under the same 

 conditions, would have been affected. 



Assuming that the colour of the animals is due to the 

 presence of pigment cells in the skin, and that the degree of 

 contraction or expansion of the individual cells determines the 

 depth of the general colour, it is probable that external heat 

 and cold are amongst the factors which modify the sha])es of 

 those cells. 



I prepared three boxes lined with white, green, and brick- 

 red paper, respectively. These I fitted with glass slides of the 

 same colours. I put both species of Agama for half aii hour into 

 each box, taking care that they received reflected light only. 

 The results were negative. I regret that circumstances did not 

 allow me to continue the experiment for a much longer period. 



When male specimens of A. aculeata are put into a bottle 



*TeiTiperature in ice-chest 2° C-, in box 40° C. 



