368 OUR RARER BIRDS 



to ask, do the Guillemot's eggs vary so considerably ? Why 

 are they allowed to present such diversity of colour, whilst the 

 eggs of most other birds are strictly confined to certain tints ? 

 We may attribute the vast variation in the colouring of the 

 Guillemot's eggs to the comparatively easy conditions under 

 which they are brought to maturity. The bird's haunts are prac- 

 tically inaccessible ; the eggs and young have few enemies, 

 and the variations which occur in the eggs are consequently 

 of small moment. Each variety, according to the Guillemot's 

 present conditions of life, has no more favour than the other ; 

 but should the conditions of their existence change, should 

 their eggs be exposed to some new danger, the variety best suited 

 to those changed conditions would doubtless be most favoured 

 — the others not so suitably coloured would, in the course of 

 time, ultimately be weeded out by a rigorous selection, and 

 the colours would most probably be confined to certain uniform 

 protective tints. The colour of birds' eggs is hereditary. A 

 Guillemot that lays a green ^gg always lays a green egg, and 

 it will transmit the faculty of laying a green egg to its off- 

 spring. This circumstance is not peculiar to the Guillemot, 

 but is common to all birds ; and the variation we see in 

 every species is the produce of certain individuals, and is 

 transmitted to their young. Hence it is easy to imagine how 

 the Guillemot's eggs would soon revert to a uniform and 

 protective tint were its conditions of life to demand it ; 

 birds laying eggs unadapted in colour to their changed 

 conditions of life would have small chance of transmitting 

 those injurious colours to a very distant posterity — would soon 

 die out completely ; and the birds that laid eggs most suitable 

 to the changed conditions and in harmony with them would 

 increase and multiply, and the colours on their eggs be 

 preserved. This, I believe, is how all eggs have got their 

 beautiful tints, and how they are preserved or changed as 

 circumstances arise. 



