278 MR. E. C. STUART BAKER ON 



said, this material is insuflScient for me to pretend that I have 

 learnt all that there is to know about Cuckoos and their eggs, but 

 it seems sufficient to prove that : — 



(1) In some genera and species evolution is only in its earliest 

 stages ; 



(2) In others it has progressed much further ; and 



(3) In certain genera and species it has arrived at perfection 

 or finality. 



Before proceeding to examine these three conditions in detail, 

 it may be as well fco propound the theory of evolution as accepted 

 by me in this connection. 



It will be probably generally admitted that the original pro- 

 genitors of Cuckoos laid white eggs and that they continued to 

 do so for a very long period after all trace of their reptilian 

 ancestry had disappeared. In fact, this persists to the present 

 day amongst those Cuckoos of the genera Centropus, Rhopo- 

 dytes, etc., etc., which are not parasitic. The belief of course 

 entails the acceptance of the theory that parasitic Cuckoos have 

 acquired their curious habit and not that non-parasitic Cuckoos 

 have grown out of it. If we accept this theory of an original 

 white or nearly white egg, it will be necessary also to accept the 

 fact that there has been some degree of evolution in almost all 

 parasitic Cuckoos' eggs, for white eggs are very rare amongst 

 Cuckoos and even those which are white are quite different in 

 character to the glossless dead white or yellow- white of most 

 reptiles' eggs. If, however, we accept the theory that all 

 Cuckoos' eggs were originally white, we have again to accept the 

 probability that all other birds' eggs were white and, this being 

 so, we should expect that the Cuckoo's Qgg would have developed 

 pari passio with the eggs of the bird in whose nest it was 

 deposited. Other birds' eggs have acquired certain coloration, 

 shapes, sizes, etc., in each case for some definite purpose which 

 has aided it to escape destruction. In some instances the 

 purpose for which the character has been acquired is obvious. 

 Many birds which lay their eggs on the ground lay such as are 

 beyond doubt protectively coloured ; some lay eggs conspicuously 

 coloured to enable the owners to distinguish their own eggs 

 among colonies ; others lay eggs so shaped that they cannot roll 

 ofi" narrow ledges of clifis ; yet others lay eggs so large that the 

 chicks emerge fledged and able to take care of themselves from 

 the start, whilst in many other instances we are still too ignorant 

 of the demands of nature to know why the characters exhibited 

 have been acquired. 



Why then have not the eggs of all parasitic Cuckoos arrived 

 at the same degree of evolution as those of other birds ? Simply 

 because Cuckoos are a modern creation and even amongst 

 Cuckoos the parasitic habit is more modern than the bird and 

 amongst those again which have acqiiired this habit, some have 

 taken to it later than others. 



All sorts of fantastic theories have been advanced as to how 



