572 Mr. C. F. M. Swynnerton on 



coloration -would probably be a sufficient differentiating 

 character. 



Merely at first sight it seems corroborative of this ex- 

 planation that the British sea-birds that form the greatest 

 nesting-colonies — the Common Guillemot^ the Kittiwake, 

 and the Black-headed, the Lesser Black -backed, and the 

 Herring Gulls — lay very variable eggs, while the apparently 

 less highly gregarious (or less abundant) Black Guillemot 

 and Common Gull, and the still less gregariously-breeding 

 Great Black-backed Gull, lay eggs that are in the first two 

 cases comparatively, in the third rather markedly, uniform. 

 But there are, of course, numerous other species even of 

 the genus Larus to be considered — some laying variable, 

 some uniform eggs, to say nothing of a Tern, Geochelidon 

 anglica, that lays variable eggs in South America, but rela- 

 tively uniform eggs in the north (Cat. Eggs B. M. i. p. 177), 

 Naturally there will often, if not always, be other and 

 complicating factors to be taken into account. That some 

 other species that lay in colonies, as Penguins and Petrels, 

 should lay eggs nearly or quite devoid of pigmentation, is, 

 however, no objection to the view, for loss of pigment migiit 

 be regarded as an alternative or eventual development Avheu 

 its presence no longer subserves the purpose either of recog- 

 nition or of concealment ^. 



Once again, an egg that had become relatively inaccessible 

 to enemies, whether as a simple matter of nesting-site or 

 through the development of pugnacity or fighting-weight 

 in its parents, might similarly not have the same need as 

 formerly for a highly distinctive appearance. In a case 

 of this kind loss of pigment might again be an alternative 

 or eventual development, for there would also be less to fear 



* This view may be applicable to many more white ^^^^ than those 

 here ineutioned. It has seemed to me, as to Mr. Pjcraft, that definite 

 selection must have been at work to produce quite the appearance of, 

 e. ^., the eggs of Woodpeckers, the strong distinctive element that 

 appears to me to be present in such eggs pointing to that conclusion ; 

 but, obviously, only definite experiment can show whether either of 

 us is correct in his view. 



