OCR Text |
Show 1906.] IN MEXICAN LIZARDS. 363 brown fields. The mid-field between the narrow stripes 3-3 is pale, bordered by rows of dark specks. Stage B.-Faint, pale brown spots appear in the first and second fields, and the mid-field becomes lighter in this way that the dark pigment is arranged in more continuous lines against the inner borders of the third stripes ; and occasionally there appears a darker central streak in the broadening mid-field. Then, with ;i length of about 70 mm., the field-spots, which are never sharp, become lighter and more numerous, and arrange themselves in one or two rows in each field, and the pale portions of the widening mid-field become greenish. Stage 0.-When the lizards approach maturity, length about 100 mm., the stripes 1 and 2, hitherto very conspicuous, become dull and lose their sharp contours. The pale field-spots become transversely confluent where they existed in double rows in ;i field, or they become enlarged transversely, so that each field is broken up into some 20 or more dark cross-bars, alternating with pale bars. Both kinds of bars encroach upon the dissolving-stripes 1, 2, and 3, whilst the remaining portions of these lines join, or merge into, the pale browrn or olive-grey, which gradually becomes the predominant ground-colour. Stage D.-- Ultimately the whole back and the sides of the body assume a very complex pattern: brown, pale brown, olive, and whitish colours, mottled or vemiculated; on the whole, however, decidedly cross-barred. The black bars are of course most conspicuous, and in some cases the black bars of the right and left sides meet across the back, producing a strikingly handsome tiger-pattern. The extent to which the longitudinal stripes disappear varies much, and in the adult of both sexes the detail of the whole complicated pattern is scarcely the same in two individuals from the same locality. A noteworthy character of these lizards is the complete absence of any pale spots except those transitory faint spots in the fields of young specimens. In this respect they differ conspicuously from C. communis and its relations, with their numerous sharply marked white, yellow, or blue spots either all over the upper surface, or at least on the rump, root of the tail, and on the thighs. The thighs of specimens from Oaxaca and Totolapan are always marbled, and the usual white stripe on the posterior side of the thigh is broken up and disappears at an early stage. CNEMIDOPHORUS MEXICANUS, var. BALSAS. (Text-fig. 83.) Number of specimens examined about 71. Within the Basin of the Balsas River, from Cuernavaca in the north to Chilpancingo in the south, the genus Cnemidophorus is, besides C. deppei, represented by a form which differs from the typical C. communis occidentalis mainly in the evolution of the dorsal pattern. It might be described as an intensified, enlarged C. gularis of which the stripes become destroyed by invasion from the fields, wdiilst they are not broken up into series of light spots, |