The Eggs of Birds 459 
or erratic motion of the egg that the curious scrawls and 
blotches upon some eggs are due. The shell is deposited 
in successive layers, and from the dim, clouded appearance 
of many colours we judge that the pigment is often partly 
concealed by the outermost layers of the shell. 
Fic. 363.—Nest and eggs of Skimmer, showing the remarkable variation in colour 
of the eggs in a single nest, heightening their resemblance to pebbles or sea- 
shells. 
Occasionally, in the eggs of birds which number only 
two in a nest, one egg will be almost white and the other 
coated with an abnormal density of pigment. In certain 
species of small birds which lay four or five eggs, one egg 
always differs remarkably from the rest. Can we not 
