DIFFICULTIES OF THE THEORY 145 



climbing trees and seizing insects in the chinks of the bark? Yet in 

 North America there are woodpeckers which feed largely on fruit, 

 and others with elongated wings which chase insects on the wing. 

 On the plains of La Plata, where hardly a tree grows, there is a 

 woodpecker (Colaptes campestris) which has two toes before and 

 two behind, a long-pointed tongue, pointed tail-feathers, suf- 

 ficiently stiff to support the bird in a vertical position on a post, 

 but not so stiff as in the typical woodpeckers, and a straight, strong 

 beak. The beak, however, is not so straight or so strong as in the 

 typical woodpeckers, but it is strong enough to bore into wood. 

 Hence this Colaptes, in all the essential parts of its structure, is a 

 woodpecker. Even in such trifling characters as the coloring, the 

 harsh tone of the voice, and undulatory flight, its close blood- 

 relationship to our common woodpecker is plainly declared; yet, 

 as I can assert, not only from my own observations, but from those 

 of the accurate Azara, in certain large districts it does not climb 

 trees, and it makes its nest in holes in banks! In certain other dis- 

 tricts, however, this same woodpecker, as Mr. Hudson states, fre- 

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

 tion 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 Fuego, the Puffinuria berardi, in its general 

 habits, in its astonishing power of diving, in its manner of swim- 

 ming 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 profoundly 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 mem- 

 bers of the great order of Hymenopterous insects are terrestrial, 

 excepting the genus Proctotrupes, which Sir John Lubbock has 

 discovered to be aquatic in its habits ; it often enters the water and 

 dives about by the use not of its legs but of its wings, and remains 

 as long as four hours beneath the surface, yet it exhibits no modi- 

 fication 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 agreement. What can be 



