Page:The Zoologist, 4th series, vol 3 (1899).djvu/204

178 duces a much larger variety than in other birds. And if we further apply to the Cuckoo the law of heritage, over and above the difference in food, the variation in the eggs would be enormously increased. Considering the manifold variety thus produced, it is quite possible that the eggs of the Cuckoo should assume a likeness to the eggs of other birds, even of such as it does not choose to lay with. We must also admit that the principle that the food of many birds, though it may not affect their own eggs, has its influence on the colouring of the eggs of their offspring, can also be applied to the Cuckoo, in the case also when it is nurtured for generations in the nests of the same species of birds whose eggs do not vary much.

We can, with some amount of certainty, assume that our Cuckoo, before he became a nesting parasite, laid monochrome blue eggs, as we see now in its near relatives the North American Coccyzus americanus and C. erythrophthalmus, which have already occasionally begun to give up rearing their own young. The blue eggs of the Cuckoo, exclusively found in the nests of the Redstart, which also lays blue eggs, may be traced to similarity of food and inheritance.