592 THE MECHANICAL FUNCTIONS. 



The Penguin, in like manner, has a wing, 

 which is, by its shortness, totally unfitted for 

 raising the body in the air : it has, indeed, re- 

 ceived a very different destination, being formed 

 for swimming. In external form it resembles 

 the anterior extremity of the turtle ; but still we 

 find it constructed on the model of the wings of 

 birds ; as if nature had bound herself by a law 

 not to depart from the standard of organization, 

 although the purpose of the structure is alto- 

 gether changed. As penguins are intended for 

 a maritime life, all their extremities are formed 

 for swimming. Their legs are exceedingly 

 short, and placed far backwards so that these 

 birds are compelled, when resting on their feet 

 on the shore, to raise their bodies in a perpen- 

 dicular attitude in order to place the centre of 

 gravity immediately above the base of support : 

 a posture which gives them a strange and gro- 

 tesque appearance. 



I have already alluded to the lengthened legs 

 and feet of the waders, the utility of which to 

 birds frequenting marshy places, and shallow 

 waters, is very obvious. Their legs are not 

 covered with feathers, which would have been 

 injured by continual exposure to wet. But 

 birds of a truly aquaticnature, have their toes 

 webbed, that is, united by a membrane, a me- 

 chanism which qualifies them to act as oars, and 

 indeed gives them a great advantage over all 



