cuckoos' eggs and evolution. 287 



of any egg in the least differing from the others. Once suspicion 

 was aroused and one knew the differences to expect, it was, of 

 course, very easy to say whether or not the egg was that of a 

 Cuckoo. The differences are those to which I have ah^eady 

 referred, viz., a very stout, heavy shell of rather coarse texture, 

 a feebly coloured yolk and a weight far greater than that of 

 similarly sized eggs of the foster-parent. 



Mr. C. E. M. Swynnerton has already referred to the question 

 of polymorphic colouring of the eggs of Cuckoos (Ibis, 1918, 

 p. 127) and also of the foster-parents, and I also have com- 

 mented on it (Ibis, 1913, p. 384). 



When we come to Hyderabad we find the most ext^raordinary 

 case of nearly completed evolution which I know of in the whole 

 history of Cuckoos' eggs. The bird selected as fosterer within a 

 very small area only a few miles across, round about this city, is 

 little Prinia socialis, a bird which lays a bright red egg, utterly 

 unlike the eggs of any of the other fosterers. Yet we find with- 

 in this tiny area, where the Cuckoo is very common, a red egg 

 has been evolved in order to ensure the preservation of the 

 species. Why Prinia socialis should have been selected as a 

 foster-parent is not very obvious, for though it is extremely 

 common in Hyderabad, breeding in every garden and hedge, yet 

 Orthoiomus also is not i-are and one would have thought would 

 have sufficed. Evidently, however, Prinia socialis is the better 

 foster-parent for local needs as it has completely ousted the 

 Tailor-Bird within Hyderabad, though only a few miles away 

 from the city the former bird is deserted and the latter again 

 imposed upon. 



It would seem that this evolution of a red egg is comparatively 

 modern, as it has not reached the stability of nwj of the eggs 

 which I have cited as examples of complete evolution. The 

 original discoverer of this red egg was Professor K. Burnett of 

 the Hyderabad College, to whom I owe a beautiful series, others 

 being taken by Col. R. Sparrow, Sergt. T. Kemp, etc. Professor 

 Burnett having found two red eggs took one and sent it to me. 

 The second was hatched and the bird, when fully fledged, also 

 forwarded to me and its identity so made certain. In collecting 

 a series, however, Professor Burnett found it much easier to get 

 fully red eggs than such as were intermediate between them and 

 the visual types of this Cuckoo's eggs. After many years con- 

 stant work by Professor Burnett and a final most generous gift 

 to me of his whole series, I have been able to link up the red 

 eggs with the others, thus giving a most perfect demonstration 

 of an egg in the course of evolution. Unfortunately these little 

 eggs fade very rapidly, possibly becaicse of their recent evolution, 

 and neither plates, magic-lantern slides, nor the eggs themselves, 

 give a proper idea of their beautiful colouring when fresh. 



With this example before us it hardly seems necessary to 

 labour further the question of whether Cuckoos' eggs are still 

 undergoing some phase of evolution, but in discussing the 



