288 MR. E. C. STUART BAKER ON 



evolution of the eggs of our Common Cuckoo, Guculus canorus, 

 the point will repeatedly come up. Cuculus canorus, which may 

 be taken as the type of Cuckoo in which evolution is most back- 

 ward, is the Cuckoo with the greatest range of all Cuckoos, 

 ranging practically throughout Europe and Asia as well as 

 through much of Africa. The geographical races with which I 

 am best acquainted are C. c. canorus, breeding in Europe, O. c. 

 telephonus, breeding in Western and ISTorthern Asia, and 

 G. c. bakeri, breeding in the Eastern Himalayas, Burma and, 

 probably, Western tropical China where the mountains are high 

 enough, i. e. 5000 feet and over. The degree of evolution 

 obtained varies greatly in the different geographical races and, 

 moreover, it even varies greatly in individual strains in each 

 race. 



Taking first our English Cuckoo, Cuculus canorus canorus, 

 we do not find that evolution has advanced very far. The com- 

 mon fosterers cuckolded by this bird are the Wagtail, Motacilla 

 alba, the Eobin, the Reed- Warbler, the Pipits, Anthus pratensis 

 and Anthus trivialis and the Hedge-Sparrow. There is certainly 

 no example of perfected evolution in England. If we take the 

 Hedge- Accentor first, we find that there is no such thing as a 

 blue Cuckoo's egg known in England, although one or two 

 reputed eggs are in collections. The nearest approach to blue 

 eggs is probably shown by the series collected by Mr. Owen 

 round about Felsted, which are a rather pale blue-grey, sparsely 

 spotted and blotched with darker. If we examine large series 

 of eggs taken by genuine collectors with the three fosterers, 

 Pipits, Wagtails, and Reed-Warblers, we find that the Cuckoos' 

 eggs go very fairly well with all of them and also that the con- 

 trast is not very startling as between them and the Robin's eggs. 

 This looks, therefore, as if evolution had arrived at a point at 

 which an inconspicuous egg had been evolved which agrees com- 

 paratively well with the five normal fosterers, whilst in respect to 

 the Hedge-Sparrow it would appear that this bird is so extremely 

 foolish that little or no evolution has taken place, or indeed, is 

 necessary. 



A closer examination, however, of lai-ge series of eggs, although 

 it shows no case of evolution such as is found in the eggs of the 

 Cuckoos we have previously dealt with, does show signs of some- 

 thing taking place in the way of elimination of the unfit. In one 

 hundred sets of each of the five fosterers named, I find that of those 

 eggs placed in the nests of Wagtails, the majority are rather pale, 

 whilst the general trend of those placed in the nests of Pipits 

 and Reed-Warblers are rather dark. Amongst the eggs of 

 Cuckoos found in Robins' nests there are certainly a greater 

 percentage of eggs with a reddish tint, although pale ones do not, 

 as we should expect, appear to be any more numerous than dark 

 ones ; finally, with the Hedge-Sparrow we find almost any type 

 of egg, though even amongst these we get Mr. Owen's beautiful 

 series of rather bluish eggs. 



