FIFTH DAY.] INSTINCTS. 141 



supplied ; and even its means of offence and defence 

 implanted by strong and perfect instincts. I will 

 mention one fact more. Swallows, quails, and many 

 other birds migrate in large flocks when their usual 

 food becomes scarce ; and in these cases it may be 

 said, I anticipate a remark of Physicus, that the 

 phenomenon depends upon imitation, and that the 

 young birds follow the old ones, who have before 

 made the same flight. But I will select the young 

 cuckoo for an unexceptionable example of the 

 instinctive nature of this quality. He is produced 

 from an egg deposited by his mother in the nest of 

 another bird, generally the hedge-sparrow. He 

 destroys all the other young ones hatched in the same 

 nest, and is supplied with food by his foster-parent, 

 after he has deprived her of all her natural offspring. 

 Quite solitary, he is no sooner able to fly than he 

 quits the country of his birth, and finds his way, with 

 no other guide than his instinct, to a land where his 

 parents had gone many weeks before him ; and he is 

 not pressed to make this migration by want of food, 

 for the insects and grains on which he feeds are still 

 abundant. The whole history of the origin, education, 

 and migration of this singular animal, is a history of 

 a succession of instincts, the more remarkable, 

 because in many respects contrary to the usual order 

 of nature. 



