456 The Bird 
eges 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 species of bird. 
Fig. 361.—Nests of Tern 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 
