FEET AND HANDS. 523 



in the water as a fish does to help to push him along. They did not 

 use their hind limbs at all for this purpose, and these, like all unused 

 parts of the body, diminished in size and strength. In the whales 

 now existing no hind limbs are to be seen, but traces of the skeleton 

 of the hind limbs are still found imbedded in the sides of the fishlike 

 body. How small these remains of the former leg are in comparison 

 with the constantly used front foot, now a paddle, may be seen from 

 Fig. 2 A and B. 



Again, ages ago, other land animals managed to raise themselves 

 from the ground into the air, the better, no doubt, on the one hand, 

 to escape from pursuing enemies, and, on the other, to catch flying 

 insects. For supporting themselves in the air, wings of some sort 

 were necessary, and so the front legs in such animals gradually altered. 



Although none of these fir.it flying animals are now in existence, 

 we know pretty well what they were like, as impressions of their 

 bodies have been left upon slatelike rocks. They were animals in 

 many ways like reptiles i. e., belonging to the same group as the 

 crocodile, whose five-toed fore foot was illustrated in our first paper. 



In some of these first fliers all the ^.yq toes were retained; four 

 were of ordinary length, but the fifth was immensely long longer, 

 in fact, than the whole body of the animal and between it and the 

 body a skin was stretched, making a wing. 



Here we have somewhat the same method of flying as we now 

 find in the bat. In a bat's outspread wing (Fig. 3 A) the five rays of 

 the fore foot are quite clear. Four of them are joined together by 

 thin skin which stretches back to the leg and the tail. The lower 

 part of the arm and three of the rays which carry the flying skin are 

 greatly lengthened, and so a very large wing is obtained. The first 

 ray, which we might call the thumb, remains short and ends in a 

 strong claw that is of use in climbing. 



We thus, in the bat, have an animal with the fore foot extraor- 

 dinarily changed to suit it for a special manner of life i. e., for fly- 

 ing. The hind foot (Fig. 3 B), not having any new kind of work 

 to do, is much less changed. It has Rve ordinary toes ending in 

 claws, with which the bat climbs or hangs on to trees. So well fitted 

 are the hind feet for this kind of work that many bats always sleep 

 wrapped up in their wings as in a mantle, hanging on to the branch 

 of a tree, head downward. 



But not all of the first flying reptiles developed wings of stretched 

 skin. Some came to fly by means of feathered wings not unlike 

 those of birds. Fig. 4 shows the bones of the fore foot or wing of 

 a small creature called the Archceopteryx, or first feathered flier. 

 This animal had three distinct toes, each ending in a claw. Two 

 toes had thus already been lost, the fourth and fifth, which also are 



