522 POPULAR SCIENCE MONTHLY. 



FEET AND HANDS. 



By,M. BEENAED (Mbs. HENEY BEENAED). 



II. 



IN our last paper we described the feet of some of the chief groups 

 of four-footed auimals. We saw that in most of these animals 

 the four feet are very much alike, because they all have the same 

 kind of work to do that is, walking or running. But when, in con- 

 sequence of its manner of life, an animal comes to use its fore feet 

 differently from its hind feet, as the kangaroo does, we find that a dif- 

 ference arises in the structure of the two. We now have to trace 

 some of the more marked changes of this kind. 



So far, all the animals we have mentioned have been land ani- 

 mals, all needing their feet for moving in one way or another on the 

 ground. But, ages ago, some land animals changed their manner of 

 life and took to living chiefly in the water, only occasionally coming 

 on to the land, or even merely coming to the surface of the water 

 when they were obliged to breathe, for they still had lungs, which 

 needed to breathe air. To such animals (for example, seals and 

 whales) ordinary feet were partially or altogether useless; they had 

 chiefly to paddle or swim, seldom or never to walk, and, to enable 

 them to hold their own against their water enemies, their limbs 

 gradually became very much changed. 



Taking first the seal, which even now climbs on to the land, we 



see all the four feet changed into paddles, but these paddles, being 



still occasionally needed for use on land, are not very unlike the feet 



of an ordinary land animal. In Eig. 1 we see that the fore foot of 



* the seal (A) bears a considerable resemblance to his hind 



d|/ foot (B); there is some difference in length and in the posi- 



A 



Fig. 1. Fig. 2. 



tion on the body, for the hind limbs face each other at the back of 

 the body, but all four are paddles. 



Taking next the whale, which has entirely given up coming on to 

 the land, we find only one pair of paddles or changed feet. WTien 

 the land ancestors of the whale took to living in the water, they 

 probably had tails, which, by whipping the water, helped them to 

 swim, and they evidently learned to wave the hinder part of the body 



