174 Darwin and Romanes dealt with. 



and brittle, that, very possibly, if they had continued 

 to be brooded, the species would have suffered through 

 eggs broken and wasted in the effort of the brooding 

 bird to turn them over — as partially, at all events, 

 brooded eggs must be, to get any approach to equal 

 heat at all parts from the sitting bird's body. In the 

 mound the heat is equalised all over, or reaches a 

 near approach to this ; so that you have the problem 

 either (i) of eggs too brittle for brooding and ex- 

 position in an open nest ; or (2), the problem of eggs 

 having become so because for ages the birds have 

 exposed them to the mound heat, and not sat upon 

 them. Which is it ? Mr. Grant Allen does not bring 

 us much help, when in his " In Nature's Workshop," 

 in The Strand Magazine, 1899, he said, clearly 

 believing that mound-birds were found only in Aus- 

 tralia, that here we have an early form of bird that 

 had " not advanced beyond the crocodilian level" of 

 leaving its eggs in the sand to be hatched by heat ! 



But, in our idea, indeed, it is in the study of such 

 adaptations and variations that the real attraction of 

 natural history lies to the true student, redeeming it 

 constantly from anything like a vast and dry know- 

 ledge of dead things, of mere stuffed specimens, 

 which are of real value simply as they may directly 

 or indirectly aid this. 



So precisely it is, in our idea, with the cuckoos — 

 no instinct could at first have led the bird to drop its 

 egg into another bird's nest — that was contrary to its 

 instinct which was to lay its e^g in a nest that it had 

 built in a place that it had selected and prepared ; 

 and the birds that had done so would, it is to be in- 

 ferred, accompHsh as great a change again were they 



