1 1 6 Dr. H. Gadow. Evolution of the Colour-pattern [May 22, 



dissolved into rows of about 25 small, pale dots, reaching from the 

 neck to the tail. With advancing age these dotted rows become faint, 

 whilst further forwards they become more pronounced. Then they 

 enlarge slightly, approaching thereby, and ultimately neighbouring 

 spots of the rows 3 and 4 fuse with each other, so that the back 

 assumes a slightly yellow-barred appearance. 



Especially the old males, with vanishing stripes 1 and 2, and without 

 specks on the lower back, do not suggest in the slightest way that these 

 creatures started originally with 4 pale stripes. 



The underparts are more or less dark blue in old males, yellowish 

 or greenish-white, suffused with blue, in the females. The collar is 

 invariably blackish. 



CnemidopTiorus mexicanus, Peters (fig. 4, PI. 4). 



This rather large lizard is an inhabitant of the southern table-land, 

 provided its elevation remains well within the temperate zone. The 

 terrain is rather barren ; always devoid of luxurious or dense vegeta- 

 tion. During their growth these lizards pass through an extraordinary 

 series of changes in their colour pattern. 



Stage A. With 6 white stripes. The young, up to 60 mm., possess 

 three pairs of complete white stripes, sharply alternating with narrow, 

 dark brown fields. 



Stage B. Pale, faint spots appear in the fields between the stripes 

 1 2 and 2 3, and the midfield between 3 3 becomes lighter in this 

 way, that the dark pigment is arranged in tiny dots, or in more 

 continuous lines against the inner borders of the 3rd stripes ; and 

 occasionally there appears also a darker central streak. Then, with a 

 head to tail length of about 70 mm., the spots in the fields become 

 lighter, more numerous, and arrange themselves in double rows, and 

 the midfield 3 3 becomes broader and greenish. 



Stage C. When the lizards approach the length of 100 mm. the 

 double rows of field spots become transversely confluent, and the 

 lateral stripes 1 and 2, hitherto very conspicuous, become dull, and 

 lose their sharp contours. Owing to the confluence of the pale spots 

 each field is now broken up into some 20 to 22 dark cross-bars. These 

 bars become darker, sometimes black brown, and encroach upon the 

 dissolving white stripes 1, 2, and 3, whilst the remaining parts of these 

 lines join, or merge into the adjoining confluent transverse spots, 

 which are still expanding. 



Stage #. Ultimately the whole back and the sides of the body 

 assume a very complex pattern; brown, pale brown, and white 

 colours, mottled or vermiculating, in the main, however, decidedly 

 cross-barred. In some cases the black bars from the right and left 

 meet across the back. The extent to which the longitudinal pale lines 



