SWIMMING ANIMALS. 59 



so as to convert the feet into very powerful oars. Most 

 of these birds look exceeding awkward when on land, 

 and as they use both their feet and wings in diving, 

 the water is undoubtedly the element in which they 

 are most at home. Speaking of the Bed-Throated Diver 

 of Northern Europe, Mr. Dresser observes that "it 

 swims low down in the water, and when uneasy or 

 alarmed will submerge its body below the surface, 

 leaving only the head and neck in view. When it 

 dives it vanishes beneath the surface without noise or 

 flutter, and propels itself along with its wings as well 

 as its feet, frequently remaining for some time before 

 it emerges to view again." 



The most remarkable modification which birds have 

 undergone for the purposes of an aquatic life is, how- 

 ever, presented by the Penguins of the Southern Ocean. 

 These grotesque birds, some of which attain a very 

 large size, are even more upright than the Puffins, and 

 when arranged in lines on the cliffs of the Antarctic 

 lands have been compared to regiments of soldiers. 

 Their short wings, which are utterly useless for flight, 

 and have but a very limited range of motion, are con- 

 verted into flipper- like paddles, covered with short 

 bristly feathers; their only use being as additional 

 swimming organs. We have here, therefore, an instance 

 of an organ originally modified for an especial purpose 

 flight subsequently undergoing a kind of retrograde 

 modification for a totally different use, although still 

 retaining the structural peculiarities which it presents 

 in ordinary birds. Certain features in the structure of 



