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process of expulsion, and that, did the cuckoo 

 occupy the nest for the requisite period, its origi- 

 nal proprietor might return and expel her from 

 her usurped possession ; while, on the other 

 hand, by laying her egg upon the ground, she 

 can watch a favourable opportunity, and depo- 

 sit it in the nest she has selected for its recep- 

 tion. Birds, again, that climb trees in search of 

 food, as the woodpeckers, have a foot admirably 

 adapted for the purpose, two claws being placed 

 before and two behind, a construction better 

 adapted than any other to enable them to rest 

 upon the trunks and large branches. While 

 speaking of the woodpecker, I must allude to 

 another beautiful adaptation of organization to 

 its mode of life. Although its claws are long 

 and much hooked, we can easily imagine that by 

 continually clinging to a perpendicular trunk, the 

 muscles of its legs will tire and fail. Behold now 

 how nature has provided for this ! the ten quill 

 feathers of the tail are very stiff, and have sharp, 

 naked points ; when, therefore, the legs tire, it 

 bends down its tail, the sharp feathers of which 

 become opposed to the bark of the tree, and the 

 bird is thus enabled, in a great measure, to sup- 

 port itself on its tail, as if upon a seat. The tail 

 of the cormorant is also similarly composed, and 

 is used for a like purpose when the bird sits upon 

 rocks.* 



Another instance of the beautiful adaptation 

 of means to an end, is to be found in some of the 



* Drumrnond's Letters. 



