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Show 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 brown, in one or two rows. These spots become transversely confluent 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 brown bars. These short cross-bars, restricted to within their fields, often remain imperfect; so that the total effect is one of black and pale spots or patches. Meanwhile the stripes change from whitish to pale grey-green. The originally brownish 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 rule 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 groundcolour ; whilst the black portions, originally the dominant colour, are henceforth allowed to grow 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 low^er back and especially along the first stripe. These white or yellowish 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 surface.-The throat and collar are always whitish, never blue or black or mottled, but the throat is often strongly suffused with pink, especially in the adult males. Chest and abdomen are at first whitish, but they soon become suffused with blue, and the scales of the flanks and belly become with age |