76 REPTILES 



tudinally striped type of coloration. Such stripes occur in the 

 European wall-lizard (Lacerta muralis) ; but they are by no 

 means constant, and it appears that in certain cases a different 

 colour-pattern may be assumed, according to age, and perhaps 

 locality. Moreover, when such changes of pattern take place, 

 they appear to do so in a definite order, which is generally as 

 follows. First of all there are longitudinal stripes ; next these 

 stripes break up into spots, which may again coalesce into cross- 

 bars ; while, as a final change, all markings may disappear, 

 and leave the skin uniformly brown or sandy. Certain indi- 

 viduals of this species undergo all these changes of colour and 

 pattern as they pass from youth to old age ; while others stop 

 short at the second or even the first stage, and a (ew skip the 

 first or second stage and begin life in the third or fourth. As 

 a rule, these changes are most pronounced in the males ; the 

 females commencing the change at a later period of life than 

 their partners, when they may either undergo the whole trans- 

 formation or only pass through some of the stages. In all cases 

 these changes of pattern and colour commence near the tail 

 and advance forwards in a kind of wave-like manner, so that 

 the shoulders of an individual of the species may be in one of 

 the intermediate stages while the tail has attained the perman- 

 ent sandy condition. 



Very similar changes also take place in certain tropical 

 American lizards of the genera Cnemidophonts and Aweiva, 

 belonging to the family Teiidac, which is related to the 

 iguanas. In these lizards a pattern of longitudinal white 

 stripes not infrequently breaks up into spots ; this dissolution 

 commencing at the tail, and gradually advancing towards the 

 head. On the other hand, pale spots may by confluence 

 produce longitudinal light stripes. Another mode by which 

 such stripes are produced is the concentration of dark pigment 

 along the borders of a pre-existing dark band, accompanied by 

 the growth of new colourless tissue in the middle of such 

 band ; thus giving rise to one white stripe flanked by a pair of 

 dark ones. A modification of this process occurs in the case 

 of the white dorsal streak met with in some lizards, which as it 

 broadens tends to develop dark pigment along the middle line, 

 and thus eventually becomes split into a pair of white stripes 

 divided by a single dark one. Confluence of pale spots in a 



