the Coloration of Eggs. 531 



naturally continued to lay unifona white or uniform pale 

 eggs. In those species tliat have not thus concealed or 

 defended their eggs, the latter have had to supply the 

 deficiency by themselves (through Natural Selection) 

 becoming concealingly coloured. A Song-Thrush's eg^ and 

 a Plover's egg are both thus coloured, each in assimilation 

 to a different environment ; and small birds' eggs generally 

 are regarded as concealingly coloured in relation to an all- 

 concealing environment of complex lights and shadows. 

 Doves' eggs are protected through the fact that '' it is a 

 difficult matter to discern, from beneath, whether there are 

 eggs in the nest or not, while they are well hidden by the 

 thick foliage above." 



In brief, eggs with powerful parents and eggs concealed 

 by extraneous obstacles to vision are white (or uniform pale), 

 having been thus enabled to remain so j the others have 

 developed concealing coloration. 



The principle (of compensatory alternatives) that underlies 

 Wallace's explanation is, I am convinced, the correct one. 

 A species that lacks, for example, fighting- weight, must owe 

 the survival of its eggs to their concealment in one way or 

 another or to some other adequate defence or mixture of 

 defences. Beyond this his explanation seems unsatisfactory. 

 It is based on a sweeping generalization which is hardly, I 

 think, supported by the facts. As Newton truly remarks 

 and shows, by instances which might be greatly multiplied, 

 no general rule can be laid down to the effect that eggs laid 

 in holes and covered nests are of a uniform white. Numerous 

 coloured eggs are found in such situations, and coloured eggs 

 belong abundantly to powerful parents, while some coloured 

 eggs are artificially covered in the parents' absence and others 

 are closely covered by protectively coloured parents — for 

 instance, the heavily and beautifully pigmented eggs of 

 Phyllastrephus flavistriatm ; this bird is the closest sitter 

 I know. Conversely, there are white eggs that neither are 

 shielded from the vision of their natural enemies, whether by 

 close-sitting parents or other appreciable objects, nor possess 



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