A CUCKOO IN A ROBIN'S NEST 19 



ments on his part. On each of these occasions the egg 

 was pushed or carried up to the wrong or upper side 

 of the nest, with the result that when the bird jerked 

 the egg from him it rolled back into the bottom of 

 the nest. The statement is therefore erroneous that 

 the cuckoo knows at which side to throw the egg 

 out. Of course he knows nothing, and, as a fact, he 

 tries to throw the egg up as often as down the 

 slope. 



The process in each case was as follows : The pres- 

 sure of the egg against the cuckoo's side, as I have 

 said, was a constant irritation ; but the irritability 

 varied in degree in different parts of the body. On 

 the under parts it scarcely existed; its seat was 

 chiefly on the upper surface, beginning at the sides 

 and increasing towards the centre, and was greatest 

 in the hollow of the back. When, hi moving, the 

 egg got pushed up to the upper edge of his side, he 

 would begin to fidget more and more, and this would 

 cause it to move round, and so to increase the irri- 

 tation by touching and pressing against other parts. 

 When all the bird's efforts to get away from the 

 object had only made matters worse, he would 

 cease wriggling and squat down lower and lower 

 in the bottom of the nest, and the egg, forced up, 

 would finally roll right into the cavity in his back 

 the most irritable part of all. Whenever this occurred, 

 a sudden change that was like a fit would seize the 

 bird; he would stiffen, rise in the nest, his flabby 



