200 A HISTORY OF BIRDS 



deficient in coloration — fright and over-excitement having ar- 

 rested the natural secretions." Again, in birds which normally 

 lay two richly coloured eggs, it sometimes happens, as in the 

 case of two pairs of eggs of the Golden Eagle, that one egg is 

 colourless. In one instance the coloured, in the other the un- 

 coloured egg was first laid. In the matter of intensity also the 

 colour varies, increasing with age up to the bird's prime and 

 then declining. Finally, if the products of this "yellow body" 

 are simply shed into the oviduct, there to mingle with the grow- 

 ing tissues of the shell, it is difficult to account for the existence 

 of patterns of coloration, as in eggs with zones of colour or 

 streaks, for example, and still more difficult to account for the 

 existence of white eggs, since the "yellow body" will be found 

 in all cases. 



We may assume then, that however derived, this pigment 

 is deposited by the walls of the oviduct, and it would seem that 

 in many cases this deposition takes place in two different regions 

 of the duct, first on the formation of the earlier layers of the 

 shell, where little more than a slight staining is affected, and 

 later when the shell is nearly complete ; in most cases there is 

 no coloration until the egg has passed some way down the ovi- 

 duct. It would then appear that the ground colour is first de- 

 posited, and after this the peculiar markings of the particular 

 egg. When these are formed while the egg is at rest a sharply 

 defined spot is the result : but it commonly happens that the 

 deposit of pigment takes place while the egg is in motion, smears 

 and blotches being the result ; and it would further appear that 

 the egg in its passage rotates, inasmuch as these streaks and 

 lines show a decided spiral arrangement. These various evi- 

 dences of the process of coloration can be well seen in eggs of 

 many birds of prey, as well as in such strongly marked eggs as 

 those of the Guillemot, for example. 



When there is a difference in the size of the two ends of 

 the egg, as is commonly the case, the larger appears first, as 

 has been proved by experiment. 



He would be a bold man who would attempt to describe all 

 the varied hues and patterns which birds' eggs display, and his 

 labour would be lost in the interminable, repellant descriptions in 

 which such an attempt to achieve the impossible would involve 

 him. But two points must necessarily strike any one confronted 



