138 Mr. C. F. M. Svvynnerton on Rejections [Ibis, 



at once suggests an argument which might be urged by 

 critics of the view that mimicry takes place at all in the 

 eggs of heteroic Cuckoos. I have lately had letters from such 

 critics, though they did not use this argument. It is that, 

 for the most part, we see only the successful candidates in 

 each annual "examination." If we could also see the possi- 

 bility for larger numbers that were ''ploughed," we might 

 find that the great majority of the eggs laid in the nests of 

 a given host — even of a host in whose nest we rarely find a 

 wrongly-coloured Cuckoo's egg — by no means resemble its 

 own eggs, and that the alleged tendency to resemble them 

 has no existence till after the " examination.^' 



I once planned an experiment to illustrate this criticism. 

 It was checked at the outset by the general interruption of 

 my experiments, but such as there is of it will just serve my 

 purpose. Taking two Coly eggs (white), I placed each of 

 them in a different Layard Bulbul's nest. From one of 

 these nests four wrongly-coloured eggs had already been 

 ejected, but it still contained an egg of its own species and 

 form that had been adopted. Going the rounds later I 

 found that only one of these Bulbul's nests contained 

 a " Cuckoo's " egg and that this resembled the bird's 

 own. 



Conclusion. " A hundred per cent, of the eggs of Pseudo- 

 coccyx experimentor found in the nests of Pycnonotus layardi 

 resemble the eggs of the foster-parent." The actual position, 

 in this case, as we happen to know, was that only one egg 

 out of seven placed in the Bulbuls' nests was of this type, 

 the remaining 85 per cent, having been utterly unlike those 

 of the foster-parent. These represented the Cuckoos' eggs 

 that we never see. This definitely limits us, for our direct 

 evidence of mimicry, to eggs seen as soon as inserted and 

 before the foster-parents' return : for, as some of my experi- 

 ments showed, the latter sometimes remove the ofl'ending 

 egg at once — and, by flying away with it, destroy all evidence 

 of its having been there except such as is afforded by the 

 incompleteness of their own clutch. This last line of evidence 

 is fairly useful in Africa, less so in a civilised country in 



