142 TRANSITIONS OF ORGANIC BEINGS. [Chap. VI. 



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 wood- 

 pecker. Even in such trifling characters as the colouring, 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 

 districts, however, 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 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 organisation profoundly modified 

 in relation to its new habits of life ; whereas the woodpecker ot 

 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 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. 



Hs 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 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 



