302 THE STORY OF THE BIRDS 



shielded from the light of day, the Chough 

 hiding them in holes of rocks, the Grass 

 Warbler concealing its highly-spotted eggs in 

 a singular purse-like nest, the Nuthatches and 

 some of the Tits laying in holes in trees, and 

 so forth. The most plausible explanation of 

 these anomalies is that in some cases the mode 

 of nesting has undergone a change within com- 

 paratively recent time ; and certainly this is 

 borne out by the fact that, in such instances, 

 the eggs are very perceptibly paler and less 

 heavily marked than those of congeneric species 

 breeding in open and exposed nests. Oologists 

 know that the eggs of the Jackdaw and the 

 Chough are very much less marked than those 

 of the Crow or the Jay. We know that it is a 

 pretty constant rule in nature, that when once 

 any special development ceases to be functional 

 it has a very strong tendency to disappear. In 

 the case of domed nests we may almost safely 

 assume that this particular style of architecture 

 is a recent adoption, and the spotted eggs have 

 not yet lost their character. Then again, we 

 must remember that the colours of eggs are to 

 a great extent common to groups, orders, or 

 genera, as the case may be ; and then we can 

 understand why we might find a spotted egg in 



