1903.] and Orthogenetic Variation in Lizards, etc. 123 



8, 9, 10 11 stripes, all adult and breeding within a radius of a few 

 hundred yards, living under the same conditions, exposed to the same 

 enemies, namely, snakes and birds, which certainly cannot appreciate 

 the difference of one stripe more or less. 



Then there is the fact that some of the species pass, during their 

 individual life, from 6 stripes to a livery with vanishing stripes, and 

 with pale spots preponderant, and lastly to a cross-barred pattern of a 

 totally different colour. Here we cannot apply the principle of the 

 survival of the fittest, due to weeding out of those of the first year's 

 lizards which do not happen to be striped, and those of the second 

 year which do not happen to become spotted, and those of older age 

 which do not manage to assume the cross-barred pattern. There are 

 no young C. mexicanus which are not striped, but there exist in the 

 same place sexually ripe specimens which present all the changes 

 intermediate between Stages C and D, cf. p. 116. 



The secret how they manage to survive is that they take care of 

 themselves. I can assert positively that the young and the adult of 

 of C. mexicanm have different habits. They frequent open ground, 

 where the vegetation is scarce enough not to impede their running 

 about. A small lizard cannot run as fast as a large one which darts 

 and bounds away like an arrow. The young remain in the open and 

 when disturbed, after running a few yards, hide in their holes, or under 

 stones, or if the worst comes to the worst, they hide between a few 

 blades of grass which, with its strongly contrasting lights and shades, 

 conceals them sufficiently. The larger specimens dart away at a 

 furious pace, and make for the nearest hedge, shrub or bush, which 

 may be 50 yards off ; there they abide, not squatting, but in a semi-erect 

 position with their eyes upon the enemy, under the criss-cross shadows, 

 on the reddish grey ground and dry leaves. 



But we cannot imagine such a complicated concatenation which 

 implies the coming to grief of all those specimens, which at a certain 

 size or age do not happen to possess the requisite equipment. Which 

 are their enemies ? Snakes and a few birds. The turkey-buzzard and 

 the " road-runner," a ground-cuckoo, are entirely guided by the eye. 

 The snakes hunt by sight and scent, but they do not seize their prey 

 unless it moves, and I am not prepared to attribute to them much 

 appreciation of colour, which, besides, is of no avail during the night, 

 the chief hunting time of those snakes whose prey lives on the 

 ground. 



Lizards have often been used as illustrations of sexual selection. 

 The colours of the males are certainly often striking and well displayed, 

 but strong pigmentation is frequently relegated to the underparts, 

 where they are not seen ; for instance, the blue or the black on the 

 belly of C. deppei. It appears with the pairing season when metabolism 

 is at its greatest activity, and, be it added, when it is also most upset 



