98 KINSHIP OF BIRDS, AS SHOWN BY EGGS. 
brilliant pebbly regions, carrying with them the bluish, green- 
ish, creamy or drab grounds, and by that tendency to variation 
for which we can never account—a thing as mysterious as 
life itself—they here, through the agency of natural selection, 
began a mottled color-adaptation which has developed so 
highly in our shore birds, Gulls and their relations. 
Among the tree-builders, Mr. Wallace has suggested that 
the mottling might be produced by the same sort of imita- 
tion of the light and shadow spots, caused by the sun’s rays 
being strained through the foliage. But this seems too 
uncertain to satisfy us. With the egg coloration developed 
from the other way, we can see how this might slightly 
intensify the already inherited tendency of spotting and 
modify the tints. This view would tend to account for the 
blue and green grounds persisting. Iam inclined to feel, 
however, that the basis of many highly spotted eggs of tree- 
builders is purely hereditary. I cannot see, for instance, 
how natural selection could get hold of the wreath around 
the large end of so many high grade eggs, It must be the 
remains of a reversion. 
Perhaps no group of birds are akin to. so many others, 
either by progression or retrogression, as the Limicole. 
That they were closely connected to the Gulls I found out 
in an attempt to differentiate their eggs and nidification by 
mere descriptions independent of the birds, long before I 
had noted that this relationship had been asserted of their 
structure, If, as held by some, the Acide (Auks, Murres, 
Puffins, etc.) are degenerated from the Limicole, through the 
Gulls (Zaride) we may readily see why the eggs of so many 
Alcide are so heavily marked, though deposited zow in 
burrows. Here, it would seem, a circuitous route to a con- 
cealed nest is fairly indicated ; for if these eggs had gone 
directly from beneath the sand to a burrow they might have 
remained white. 
Among the Birds of Prey, the markings as noted are quite 
probably an inheritance from the ground-building habits of 
