112 Darwin and Romanes dealt with. 



Indeed, from my own observations, in conjunction 

 with those of Mr. Hancock, as given respecting the 

 young cuckoo turning out its foster-brothers from the 

 nest, I am convinced that the non-simultaneity of 

 hatching is one of the circumstances that tend to give 

 the young cuckoo much of his power : he has a 

 chance at once against eggs and young ones,. and it is 

 clear that he is keen to work upon both, so long as is 

 necessary, by his restlessness, making it impossible 

 for the foster-bird to hatch out the second half of the 

 eggs, which he inclines first of all to dispose of, as 

 was notably the case in regard to the nest observed 

 by Mr. Hancock. Absolute simultaneity of hatching, 

 that is, practically, four young birds at one moment 

 to deal with, in place of one or two, would present 

 difficulties — at least the business would be, on all 

 natural considerations, rendered longer, more hazar- 

 dous and hard. 



One fact, which was not only before Mr. Darwin, 

 but specially dwelt on by him, might have led him to 

 revise his whole passage relative to the cuckoo in 

 eighth chapter of Origin of Species had he been any- 

 thing of a thinker, which he was not. This fact was 

 the stay of young cuckoos in our country up to the 

 month of September. It might surely have struck 

 Mr. Darwin that if the young ones could stay, the old 

 ones surely could. It did not strike him to ask any 

 question in connection with that, therefore we say he 

 was not a thinker. It seems to have struck another 

 writer with great force : 



" The cuckoo's early migration can hardly be part 

 of the cause, it is rather a correlated effect. The 

 cuckoo leaves us early because its parental instincts 



