Why Cuckoos' Eggs are heavy. 151 



degree kept even ; otherwise there would be no 

 balance at all. The more easily duped birds would 

 gradually decrease, or even be exterminated, and the 

 cuckoos would so increase, that the inroads, even on 

 doubtful birds, would go on apace. If there is any- 

 thing in this, it might go some way to account for the 

 existence or the increase of unmatched eggs : account 

 for the evidences in certain directions of the cuckoo's 

 methods becoming more and more patent and observ- 

 ahle — and account, too, for the very belated discovery 

 in our country of the most remarkable points in the 

 life-history of this most extraordinary bird. Thus, 

 instead of there being any ground for Mr. Romanes' 

 assumption, it is proved almost to demonstration that 

 Nature is, as Goethe says, very lavish of life, but also 

 very careful to preserve her balance : leading up to 

 the conclusion that the results of true study of her 

 are exactly in the teeth of such statements as that of 

 Mr. Romanes now specially under notice, and some of 

 those even of Mr. Darwin. 



Yet Mr. Romanes, as we have seen, actually says 

 that, " with the one doubtful and not sufficiently in- 

 vestigated exception — that of cuckoos adapting the 

 colour of their eggs to that of the eggs of the foster- 

 parents — there is nothing connected with these in- 

 stincts that presents an}' difficulty to the theory of 

 evolution." Surely, there is at least this one other, 

 referred to most unreservedly by Dr. Bowdler Sharpe 

 — the cuckoo now lays an &gg which, compared with 

 that of other birds, is of but a quarter the size that 

 it should be, though it is, compared with other eggs 

 of the same size, heavy. How is this, and how has 

 it been brought about ? Did the bird always lay 



