192 SKETCHES OF BIRD LIFE. 



While admitting, therefore, the tendency which 

 certain habits have to become hereditary in certain 

 animals, we feel compelled to reject the application 

 of this principle in the case of the Cuckoo, on the 

 ground that it can only hold good where the habit 

 results in an advantage to the species, and in the 

 present instance we have no proof either that there 

 is an advantage, or, if there is, that the Cuckoo is 

 sensible of it. 



Touching the question of similarity between 

 eggs laid by the same bird, Professor Newton says : 

 " I am in a position to maintain positively that 

 there is a family likeness between the eggs laid by 

 the same bird" (not a Cuckoo) "even at an interval 

 of many years," and he instances cases of certain 

 Golden Eagles which came under his own observa- 

 tion. But do we not as frequently meet with 

 instances in which eggs laid by the same bird are 

 totally different in appearance ? Take the case of a 

 bird which lays four or five eggs in its own nest 

 before it commences to sit upon them for example, 

 the Sparrow-hawk, Blackbird, Missel-Thrush, Car- 

 rion Crow, Stone Curlew, or Black-headed Gull. 

 Who has not found nests of any or all of these in 



