282 THE STORY OF THE BIRDS 



to find one egg in the clutch differing con- 

 siderably from the rest. In some of the Birds 

 of Prey this peculiarity is very striking, and in 

 no species more so perhaps than in certain 

 Eagles and Vultures. In the Golden Eagle, 

 for instance, one of the two eggs is generally 

 much more heavily spotted than the other. 

 This is often attributed by collectors to the 

 fact that the colour pigments were all exhausted 

 in decorating one egg only ; but it has been 

 proved many times that the first egg has been 

 the one in which markings were wanting. It 

 may be that the colour-producing glands 

 had not sufficiently recovered their functions 

 peculiar to the laying season before the first 

 egg was deposited. We have sometimes re- 

 marked a similar peculiarity in the eggs of 

 various Passeres, the first egg laid being much 

 less handsomely marked than those that suc- 

 ceeded it. 



For the exact composition of the colour pig- 

 ments on eggs we are indebted to the re- 

 searches of Dr. Sorby, who ascertained by 

 the aid of spectrum-analysis that no less than 

 seven substances were found in them. These 

 were named Oorhodeine, Oocyan, Banded 

 Oocyan, Yellow Ooxanthine, Rufous Ooxanthine, 



