WINGED REPTILES. 315 



On the other hand, the Squamata (so called because of the scaly 

 covering which characterizes them) are the most modern of all reptiles. 

 They number now more than thirty-four hundred species, about equally 

 divided between the lizards and snakes, the only modern representatives 

 of the order. In the remote past so far as we can trace the broken line 

 of descent, the ancestral forms had but a single conspicuous offset, the 

 rapacious mosasaurs, which had, however, a comparatively brief ex- 

 istence. The lizards, like the snakes, probably go back little or no fur- 

 ther than the Age of Mammals. They are, with few exceptions, terres- 

 trial animals of small size and inoffensive habits; the largest living 

 examples scarcely exceed six feet in length, though within the period of 

 man's existence there have been lizards five or six times as long. 



Snakes or serpents, the latest, and in many respects the most special- 

 ized, of all reptiles, have not yet reached the culmination of their 

 development, a statement which perhaps may not be truthfully made of 

 any other group of reptiles. Their geological history is insignificant 

 and scanty. The venomous serpents especially present the latest modi- 

 fications of reptilian structure, perhaps the very latest antecedent to the 

 final extinction of the whole class. 



No reptiles at the present time walk erect, as did many of the extinct 

 kinds. Their progression is essentially a crawling one, their legs, when 

 present, serving more for propulsion than support. The only exceptions 

 to strictly arboreal, terrestrial or aquatic habits among living reptiles are 

 found in the curious and beautiful little flying lizards, or ' flying 

 dragons,' of the Malayan region. In these reptiles, the flattened body is 

 provided with a broad, wing-like expansion of the skin of its sides, sup- 

 ported by the elongate, movable ribs, and capable of being folded up, 

 fan-like. Similar membranous expansions are also found on the sides 

 of the throat. By these means the creature, which lives for the most 

 part among the tree tops, rarely descending to the ground, is capable of 

 certain aerial movements, though not of true flight. In describing its 

 habits a writer has said : "As the lizard lies in shade along the trunk of 

 a tree, its colors at a distance appear like a mixture of brown and gray 

 and render it scarcely distinguishable from the bark. There it remains 

 with no sign of life, except the restless eyes, watching passing insects, 

 which, suddenly expanding its wings, it seizes with a sometimes con- 

 siderable, unerring leap." Their flight through the air is very swift, 

 so swift that the expansion of the parachute-like membrane may almost 

 escape notice. As in the flying fishes, flying lemurs and flying squirrels, 

 there is not true flight — a power possessed by no living back-boned ani- 

 mals except birds and bats. 



Altogether the direct antecedents of the reptiles now living, that is 

 the crocodiles, turtles, lizards and snakes of the past, took no important 

 part in the great Age of Eeptiles. They have existed all these millions 



