COLORATION AND ITS INTERPRETATION 79 



on the under-parts. These blue blotches, and the brighter 

 tints generally, being placed on the under surface of the body- 

 are more or less completely hidden when the reptiles are 

 crouching on the ground, and only become visible when the 

 head and body are elevated under the influence of excite- 

 ment. At such times the blue or purple on the throat of the 

 males is conspicuous, although that on the flanks is less notice- 

 able. This type of colouring is therefore evidently a secondary 

 sexual character. Generally the upper parts are some shade of 

 brown, and adapted for protective resemblance when the lizards 

 are crouching. Here it may be noticed that the bright blue 

 spots on the flanks of the European eyed lizard (Lacerta 

 ocellata) have the same situation as the lateral blue blotches of 

 the males of Sceloporas ; and if, as is probable, they are brighter 

 in males than in females, they may be regarded as sexual colour- 

 features. From their position, it may be inferred indeed 

 that these blue blotches have little to do with concealment 

 although, as already mentioned, the " vermiculated " black and 

 yellow colour-pattern of the back of these lizards is protective. 

 Still, as stated below, the whole colouring may at a short dis- 

 tance blend into an inconspicuous blur. 



The American blue-tailed skink (Eumcccs quinqudineatus) 

 offers an example of pattern and colour-change dependent upon 

 sex and age. In the young the tail is bright blue and the body 

 blackish with five yellow stripes. As this lizard matures the tail 

 fades to sombre grey, the body changes from black to brown, 

 the stripes (in the males at any rate) entirely disappear, and 

 the head, in the same sex, assumes a bright red hue. Formerly 

 the adult was regarded as a distinct species. 



Again, in the aforesaid terrestrial iguana, Scelopovus aos- 

 teromus, the adults show a broad dark lateral band running 

 backwards from in front of the fore-limb along the flank, while 

 in the young the large patch in front of the fore-leg is frequently 

 disconnected from the lateral band. In 5. biseriatus the throat, 

 the middle of the under surface, and the lower side of the thigh 

 in old males are often black, while in younger individuals they 

 are greyish or bluish. In the case of one species of horned 

 toad {Phrynosoma coronatum) all the markings are much more 

 distinct in the young than in the adult ; the small spots on the 

 raised portion of the scales of the head in the young gradually 



