ADAPTATIONS 113 



Moloch. On the other hand, in some of the tree-snakes, such 

 as those of the Old World genus Dendrophis, the body tends 

 to the compressed type, thus displaying another adaptive 

 parallel to lizards, in which, as we have seen, the arboreal 

 species have a compressed form of body. The tree-snakes of 

 the genus above-mentioned have, however, a special modifica- 

 tion for climbing, this taking the form of a pair of keels flanked 

 by notches on the scales of the under side of the body ; by the 

 additional hold on the bark thus afforded these snakes are able 

 to glide along branches in a nearly straight line, instead of 

 having to pursue the usual sinuous course. 



Complete assumption of the gliding type of bodily contour 

 occurs in the more typical members of the snake-lizards of the 

 family Anguidcs. Indeed the slow-worm (Anguis fragilis) and 

 the glass-snake or scheltopusik (Ophisaurus apus) are universally 

 regarded in popular estimation as true snakes, from which they 

 may be at once distinguished by the presence of movable eyelids, 

 as well as by the brittle tail, which can readily be snapped in 

 twain. The mention of eyelids calls for the remark that the 

 name "blind-worm " is a misnomer, the creature having per- 

 fectly well-developed and functional, although small, eyes. 

 Traces of the shoulder and pelvic girdles are always met with 

 in the family, but the limbs may be either fully developed or 

 entirely aborted. The slow-worm, in which the body is 

 entirely covered with small cylindrical scales like those of the 

 blind-snakes, exhibits the extreme degree of specialisation, the 

 limbs being entirely aborted. On the other hand, in the glass- 

 snake, in which the body is greatly elongated although the 

 head is that of a typical lizard, there are vestiges of the hind- 

 limbs in the form of a pair of small, half-concealed spines on 

 each side of the vent. When, however, we come to the species 

 of the tropical American genus Gerrhonotus we find both pairs 

 of limbs fully developed, each foot having five complete toes. 

 We thus have circumstantial evidence of the loss of the limbs 

 in certain species within the limits of the family, although it is 

 not to be supposed that Gerrhonotus represents the actual type 

 from which the snake-like forms have been evolved. In 

 summer both slow-worms and glass-snakes live chiefly among 

 grass and leaves, although in autumn many individuals of the 

 former make burrows in which they pass the winter. 



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