Adaptations to Environment 131 



obscure, but it is probable that insects could run, leap, and para- 

 chute before they could actually fly. 



The extinct Flying Dragons or Pterodactyls had their 

 golden age in the Cretaceous era, after which they disappeared, 

 leaving no descendants. A fold of skin was spread out from the 

 sides of the body by the enormously elongated outermost finger 

 (usually regarded as corresponding to our little finger) ; it was 

 continued to the hind-legs and thence to the tail. 



It is unlikely that the Pterodactyls could fly far, for they 

 have at most a weak keel on their breastbone ; on the other hand, 

 some of them show a marked fusion of dorsal vertebra, which, 

 as in flying birds, must have served as a firm fulcrum for the 

 stroke of the wings. The quaint creatures varied from the size 

 of a sparrow up to a magnificent spread of 15-20 feet from tip to 

 tip of the wings. They were the largest of all flying creatures. 



The bird's solution of the problem of flight, which will be 

 discussed separately, is centred in the feather, which forms a 

 coherent vane for striking the air. In Pterodactyl and bat the 

 wing is a web-wing or patagium, and a small web is to be seen on 

 the front side of the bird's wing. But the bird's patagium is 

 unimportant, and the bird's wing is on an evolutionary tack of 

 its own a fore-limb transformed for bearing the feathers of 

 flight. Feathers are in a general way comparable to the scales of 

 reptiles, but only in a general way, and no transition stage is 

 known between the two. Birds evolved from a bipedal Dinosaur 

 stock, as has been noticed already, and it is highly probable that 

 they began their ascent by taking running leaps along the ground, 

 flapping their scaly fore-limbs, and balancing themselves in 

 kangaroo-like fashion with an extended tail. A second chapter 

 was probably an arboreal apprenticeship, during which they made 

 a fine art of parachuting a persistence of which is to be seen in 

 the pigeon "gliding" from the dovecot to the ground. It is in 

 birds that the mastery of the air reaches its climax, and the mys- 

 terious "sailing" of the albatross and the vulture is surely the most 



