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The Bird 



eggs of the ancestors of these birds for the sake of protec- 

 tion, all need for it is now lacking, and as an apparent 

 result the various hues seem to have run riot. One may 

 place a hundred murres' eggs side by side and find no two 

 alike, while the extremes would never be recognized as 

 belonging to the same spefcies of bird. 



Fig. 3fil. — Nests of 'Pern and Skimmer. 



Another instance of extreme variability in the colour 

 of eggs and an instance of intensely interesting import is 

 found in the English Cuckoo, which may be taken as an 

 example of species which are parasitical, — in the sense 

 that the females make no nest of their own, but deposit 

 their eggs in the nests of other birds, the young being thus 



