198 Major R. F. Meiklejoliu on the [Ibis, 



Egg-coloration. 



When we proceed to deal with Dr, Rey's conclusions iu 

 detail we find that the 1st, 3rd, 4th, and 5th deal Avith 

 the question of " egg-coloration/' and here again we are 

 confronted with a difficult problem, full of rather contra- 

 dictory facts, which are not easy to fit into any tlieory, but 

 wl)ich constitutes an important feature in the consideration 

 of the Cuckoo's nesting-habits. And as the coloration of 

 Cuckoos' eg:gs is subject to the same rules as those of other 

 birds, a short digression seems justified. 



So far as I am aware, the causes governing the colora- 

 tion of eggs are unknown, though many theories have been 

 adduced. If we assume that birds are descendants from 

 reptiles, as there seem good reasons for doing, it follows 

 tliat originally their eggs were white or yellowish-white, 

 and, consequently, that birds laying such eggs have remained 

 true to type, while such species as lay brightly-coloured eggs 

 have departed most widely from it. 



We may also notice that such species as lay in concealed 

 places, like the reptiles, have, as a rule, remained true to 

 type, wliile others whose nesting-habits have departed widely 

 from those of their progenitors have also changed greatly in 

 the colour of the eggs, possibly under the influence of the 

 law of adaptation. 



Professor Alfred Newton formed the opinion that circular 

 markings on the egg-surface are deposited on the shell a 

 short time before extrusion, and that, as the egg progresses 

 through that part of the oviduct in Avhich it receives the 

 colouring matter, many specimens get smears or blotches, 

 which are protracted in some direction. He therefore con- 

 sidered that the circular spots denote the deposition of 

 l)igment while the egg is at rest, while blurred markings 

 occur while it is in motion, and such motion appears to be 

 forward and rotary, often producing spiral smears. And as, 

 on nearly all occasions, the larger end is protruded first, 

 it is, as a rule, the more heavily marked ; but when, as 

 sometimes occurs, the reverse is the case, the small end is 



