CiiAP. VI. OF ORGANIC BEINGS. 177 



Mexican Colaptes has been described by Do Saussurc as boring 

 holes into hard wood in order to hiy up a store of acorns, but 

 for what use is not yet known. 



Petrels are the most ar-rial and oceanic of l)inls, l)ut in the 

 quiet sounds of Tierra del Fucf^o, the Pulhnuria berardi, in its 

 l^eneral habits, in its astouisliinii^ power of divinjr, its manner 

 of swiinminij;-, and of flying when made to take lliglit, would be 

 mistaken by anyone for an auk or a grebe; nevertheless it is es- 

 sentially a petrel, but with many parts of its organization pro- 

 foundly modified in relation to its new haliits of life ; Avhereas 

 the woodpecker of L:i Plata has had its structure only slightly 

 modified. In the case of the Avater-ouzcl, the acutest observer 

 by examining its dead body would never have suspected its 

 sub-aquatic hal)its; yet this binl, which is allied to the thrusli 

 familv, wholly subsists by diving — using its wings under 

 \yater, and grasjiing stones with its feet. AH the members of 

 the great order of Hymenopterous insects are terrestrial, ex- 

 cepting the genus Proctotrupes, which Sir J(jhn Lubbock has 

 recently 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 not the least modification in its structure can be detected 

 in accordance Anth such abnormal habits. 



He who believes that eacli 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 at all in 

 agreement. What can be jilaincr than that the webbed feet of 

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

 land geese with webbed feet which rarely or never 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 jilaincr than that the long toes, not furnished with 

 membrane, of the Grallatores are formed for walking over 

 swamps and lloating plants? The water-hen and landrail are 

 members of this order, yet the first is nearly as acjuatic as the 

 coot, and the second nearly as terrestrial as the quail or ])ar- 

 tridge. In such eases, and many others could be given, habits 

 have changc^d Avithout a corresponding change of structure. 

 The webbed feet of the upland goose may be said to have be- 

 come rudimentary in function, though not in structure. In the 



