TRANSITIONS OF ORGANIC BEINGS. 159 



Hence thk Colaptes, in all the essential parts of its structure, 

 is a woodpecker. Even in such tritiing characters as the col- 

 oring, 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 obser- 

 vations, but from those of the accurate Azara, in certain 

 iarge 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 hab.ts 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, 

 m 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 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 members of the great order of Hymen- 

 opterous insects are terrestrial, excepting the genus Procto- 

 trupes, 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 modifi- 

 cation 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 agree- 

 ment. 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 sur- 

 face of the ocean. On the other hand, grebes and coots are 

 eminently aquatic, although their toes are only bordered by 



