TRANSITIONS OF ORGANIC BEINGS 189 



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 swimming and of flying when made to take flight, 

 would be mistaken by any one for an auk or a grebe; never- 

 theless 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 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 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 be- 

 neath 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 agree- 

 ment. What can be plainer than that the webbed feet of 

 ducks and geese are formed for swimming? Yet there are up- 

 land 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 Grallatores are formed for walking 

 over swamps and floating plants? — the water-hen and land- 

 rail are members of this order, yet the first is nearly as 

 aquatic as the coot, and the second nearly as terrestrial as 

 the quail or partridge. In such cases, and many others could 

 be given, habits have changed without a corresponding change 



