“2. Eggs laid in domed nests certainly do not need protective colouring, yet many of these are coloured.
“3. The same is true of many eggs laid in holes in trees or in buildings.
“4. The protective resemblances of eggs which are laid in the open are apparent to everyone, which certainly is not true of those deposited in nests.
“5. Many birds lay eggs which exhibit very great variations.
“6. Some birds lay eggs of different types, and these sometimes differ from one another so greatly that it is difficult to believe that they could have been laid by the same species.”[9]
7. It not infrequently happens that one species lays in the disused nest of another, and the eggs of the latter are often very different in colouring from those of the former.
We have up to the present considered the theory of general cryptic colouration, which declares that the majority of creatures are so coloured as to be inconspicuous. We have still to deal with the hypothesis of special cryptic colouring.
Certain animals look, when resting, very like an inanimate object, such as a dead leaf or a twig. This resemblance is said to be the result of natural selection, since it enables its possessors to escape destruction; they are seen, but mistaken for something else.
The classical examples of this kind of protective colouring are furnished by the Kallimas or leaf-butterflies, which display an extraordinary resemblance to dead leaves.
Other examples are the stick-insects and the lappet moth, which looks like a bunch of dry leaves. It is needless to multiply instances. In every work on animal colouration numbers of such cases are cited.