TRANSITIONS OF OBQANIO BEINGS. 169 



this same woodpecker, as Mr. Hudson states, frequents 

 trees, and bores holes in the trunk for its nest. I may 

 mention as another illustration of the varied habits of this 

 genus, that a Mexican Colaptes has been described by De 

 Saussure as boring holes into hard wood in order to lay up a 

 store of acorns. 



Petrels are the most aerial and oceanic of birds, but, 

 in the quiet sounds of Tierra del Puego, the Puffinuria 

 berardi, in its general habits, in its astonishing power of 

 diving, in its manner of swimming and of flying when 

 made to take flight, would be mistaken by any one 

 for an auk or a grebe; nevertheless it is essentially a 

 petrel, but with many parts of its organization pro- 

 foundly modified in relation to its new habits of life; 

 whereas the woodpecker of La Plata has had its structure 

 only slightly modified. In the case of the water-ouzel, 

 the acutest observer, by examining its dead body, would 

 never have suspected its sub-aquatic habits; yet this bird, 

 which is allied to the thrush family, subsists by diving — 

 using its wings under water, and grasping stones with its 

 feet. All the members of the great order of Hymenopter- 

 ous insects are terrestrial, excepting the genus Procto- 

 trupes, which Sir John Lubbock has discovered to be 

 acquatic in its habits; it often enters the water and dives 

 about by the use not of its legs but of its wings, and re- 

 mains as long as four hours beneath the surface; yet it 

 exhibits no modification in structure in accordance with 

 its abnormal habits. 



He who believes that each being has been created as we 

 now see it, must occasionally have felt surprise when he 

 has met with an animal having habits and structure not in 

 affreement. What can be plainer than that the webbed 

 feet of ducks and geese are formed for swimming? Yet 

 there are upland geese with webbed feet which rarely go 

 near the water; and no one, except Audubon, has seen 

 the frigate-bird, which has all its four toes webbed, alight 

 on the surface of the ocean. On the other hand, grebes 

 and coots are eminently aquatic, although their toes are 

 only bordered by membrane. What seems plainer than 

 that the long toes, not furnished with membrane of the 

 G-rallatores, are formed for walking over swamps and float- 

 ing plants.'' The water-hen and landrail are members of 



