152 Darwin and RoDiaiies dealt ivitJi. 



such an eg^ even when in those days its habits were 

 like those of its American congeners ? If not, how 

 did it come to effect such an extraordinary change as 

 to get rid of three-fourths the area of an egg without 

 any the least injury to the vitality or to the size of 

 the young bird that is to come from it ? That is 

 quite as remarkable a point as anything about it, and 

 raises a problem exactly analogous to that of colour- 

 ation of eggs. If the reducing of the size of the eggs 

 was a very, very gradual process, as under evolution 

 it ought to be, how was it that small birds were, 

 through ages, taken in with such a monster egg in 

 comparison with their own — the more that even now, 

 when the egg is so reduced in size and some at least 

 vague effort made to vary colour to imitate other 

 eggs, certain birds are apt to detect it, throw it out, 

 or build it over so as not to hatch it ? Surely most 

 birds have, some conception of size if they have 

 not of colour ; besides this, to brood an egg of such 

 dimensions would be hurtful and inconvenient for 

 very small birds to sit on and to turn over, as they 

 must at intervals turn all the eggs over. Such a size 

 of egg, moreover, would militate against the hatching 

 of certain of the smaller eggs at the proper time by, 

 of course, causing the bird to sit too high above them 

 to keep them all equally warm. Again, if birds — 

 especially small birds — could be thus deceived with 

 one egg of a natural size, or nearer to a natural size, 

 for the cuckoo through long, long ages, what, then, 

 was the necessity for reduction in size and efforts 

 after contrasted colouration ? This would then be 

 purely a waste of energy, and still is so. 



Or did the cuckoos of the ages far back go on re- 



