256 MENTAL FACULTIES sec. 



opinion is the deliberate artfulness with which the turkey 

 already mentioned, not yet a day and a half old, hunted flies. 

 He aimed carefully with his beak at flies and other small 

 insects witliout actually pecking at tliem, and while he did 

 this his head trembled like a hand which one tries to hold 

 motionless by an effort. I observed and recorded this when 

 I did not yet understand the meaning of it ; for not till 

 afterwards did I discover that it is an invariable habit of the 

 turkey when he sees a fly sitting on any object to creep 

 slowly and with cautious steps to the unsuspicious insect, 

 and to stretch out liis head very carefully and surely to the 

 distance of about an incli from his prey, which he then 

 seizes with a sudden stroke." 



The Instinct of the Cuckoo in Laying her Eggs in other 



Birds' Nests 



This instinct has been much discussed on account of its 

 peculiarity, especially since Darwin gave an explanation for 

 it. Darwin says in tlie Origin of Species: "It is supposed 

 by some naturalists that the more immediate cause of the 

 instinct of the cuckoo is that she lays her eggs not daily, but 

 at intervals of two or three days, so that if she were to make 

 her own nest and sit on her own eggs, those first laid would 

 have to be left for some time unincubated, or there would be 

 eggs and young birds of different ages in the same nest. 

 This explanation is not sufficient, for the American cuckoo 

 makes her own nest, lays her eggs in it, and has eggs and 

 young successively hatched, all at the same time. She also 

 lays her eggs occasionally in other birds' nests." Darwin, as 

 is known, then supposes that the ancient progenitor of our 

 European cuckoo had the habits of the American cuckoo, 

 and that she occasionally laid an egg in another bird's 

 nest. " If the old bird profited by this occasional habit 



