35 [Vol. xxxi. 



(2) That a process of adaptation in colour was most 

 undoubtedly being undergone. 



(3) That evolution in shape was not indicated. 

 Amongst the series exhibited, Mr. Stuart Baker showed 



that in some cases^ as in the eggs of Coccystes and of 

 Hierococcyx varius, adaptation in colour had reached great 

 perfection and that it was only in abnormal cases that the 

 Cuckoo's egg did not agree with that of the foster-parent. 

 With other eggs it was manifest that evolution was still in 

 progress, the most noticeable case in this respect being the 

 marvellous fjdaptation obtaining in the eggs of Cuckoos of 

 the genus Cacomttntis. Whilst asserting that it could hardly 

 be doubted that evolution in adaptation was in progress, 

 Mr. Stuart Baker repeatedly emphasized the fact that this 

 evolution was brought about not by creation, but by elimina- 

 tion. It seemed to him that amongst the foster-parents 

 selected by the Cuckoo to hatch its eggs birds were occa- 

 sionally met with sufficiently clever to discover the difference 

 between their own eggs and that of the Cuckoo. The more 

 startling the difference the easier it would be for the foster- 

 parent to exercise this power of discrimination, and so by 

 very slow degrees those individual Cuckoos whose eggs were 

 unlike the eggs of any foster-parent would gradually die out, 

 whilst those laying eggs more like the eggs of the host would 

 persist. 



Evolution was brought about by the foster-parent and 

 not by the Cuckoo. 



Another important point alluded to was that if evolution 

 was admitted, it was possible to estimate the comparative age 

 of the various genera amongst parasitic Cuckoos. Thus 

 Cuculus canorus and its subspecies were probably of modern 

 origin, only commencing to evolve eggs of any particular 

 colour and as yet quite indifferent as to what species of host 

 they might select. Coccystes, on the contrary, would appear 

 to be a very ancient form of Cuckoo, in which evolution in 

 the colour of the eggs had been perfected and the number of 

 foster-parents reduced to species of one or two genera, all 

 laying similarly coloured eggs. 



