1906.] IN MEXICAN LIZARDS. 365 



and to the fact that many specimens stop short at a stage, while 

 others, in other localities, pass through and beyond, when they 

 have reached the corresponding size or age. 



The young start with 6 pale, sharply marked whitish stripes 

 upon very dark, almost black ground, but the mid-field is grey, 

 with inner dark borders, and this mid-field is frequently subdivided 

 into one or two greenish stripes, so that the total number of 

 stripes is 7 or 8. The fields are originally uniform dark, blackish ; 

 then turn up pale field-spots, mostly light brown or reddish 

 bro-wn, in one or two rows. These spots become transversely con- 

 fluent within each field, first in the lateral field and in field I., 

 then in field II. ; and thus the fields are cut up into irregular 

 alternating black and bi'own bars. These short cross-bars, restricted 

 to within their fields, often remain imperfect ; so that the total 

 efl:ect is one of black and pale spots or patches. Meanwhile the 

 stripes change from whitish to pale grey-green. The originally 

 Ijrownish spots and bars are likewise liable to change colour. 

 Either they become dull white, especially on the lateral field, or 

 they become grey-green, especially in fields II. and III. ; those in 

 field I. retain their brown colour longest. 



As a ride the stripes remain intact unless they are joined by 

 the spreading grey-green bars. This fusion of the stripes 

 with the spreading greenish patches and bars imitates the 

 tendency of turning the grey-green into the prevailing groimd- 

 colour ; whilst the black portions, originally the dominant 

 colour, are henceforth allowed to groAv into narrow cross-bars, 

 which can spread over several fields by crossing the self-effacing 

 stripes. The ultimate result is a moderate black tiger-barring 

 upon an ever-increasing green-grey ground, which itself tends to 

 become duller and darker. This condition is in C. mexicanus var. 

 balsas reached but rarely, for instance by a few specimens from 

 Chilpancingo, Rio Balsas, and Iguala. 



Another'complication initiates what becomes the characteristic 

 feature in C. communis. The thighs, the root of the tail, and the 

 rump develop numerous small but conspicuous whitish spots or 

 specks, which are partly the modified original field-spots, and, most 

 important, white or yellowish spots which appear in the original 

 pale stripes, hand in hand with a blackening of the ground-colour. 

 This tendency to spottiness gradually extends from the rump upon 

 the lower back and especially along the first stripe. These white 

 or yelloAvish spots on thighs, root of tail, rump, and lower back 

 show no tendency to fuse with each other ; on the contrary, they 

 seem to become more pronounced and more numerous with age. 

 Such specimens, all adult, are some of those from Cuernavaca, 

 Iguala, and Chilpancingo (text-fig. 83 D, E, F). 



Colour of under stirface. — The throat and collar are always 

 whitish, never blue or black or mottled, but the throat is often 

 strongly sufi\ised with pink, especially in the adult males. Chest 

 and abdomen are at first whitish, but they soon become suffused 

 Avith blue, and the scales of the fianks and belly become with age 



