144 BIRD BEHAVIOUR 



ternal impressions would tell us that this is ]ust 

 what one might expect, but the white eggs of the 

 equally sanguinary Owls would confute him. 



But the existence of such meaningless coincidences 

 should make us careful in assigning a survival value 

 to every modification of form and colour in either 

 bird or egg ; the subcorneal shape of the Guille- 

 mot's egg, for instance, certainly renders it less 

 likely to roll oflE the ledge on which it is laid, but 

 then one parent bird or the other is always on it, 

 and the peg-top shape of the eggs of Plovers and 

 shore-birds, although it facilitates packing in the 

 cross-shaped arrangement, points all inwards, which 

 the sitting bird affects for them, may be merely 

 incidental and not specially evolved. 



Sometimes there seems to be no reason whatever 

 for the peculiarities of an egg ; why, for instance, 

 should the curious Pink-headed Duck of India 

 {Rhodonessa caryophyllacea) lay, in an ordinary Duck- 

 nest, eggs which in colour, gloss, and roundness 

 remind one of a set of billiard-balls ? Then as to 

 markings and tint, no reason has been given why 

 the Guillemot should lay eggs so extraordinarily 

 variable in these respects, or why birds which lay 

 coloured or variegated eggs should, generally speak- 

 ing, exhibit so much difference in their output, 

 as compared with the uniformity of their plumage. 



Broadly speaking, one may expect in any species 

 laying a variegated egg specimens lightly and 

 heavily spotted, and others with fairly evenly 

 distributed markings contrasting with some in 



