Page:Popular Science Monthly Volume 76.djvu/551

Rh, the female returned with an insect, and resumed her brooding again.

The instincts of the parent and young are of the lock and key order. Each acts as a stimulus to the other, and the reward of satisfaction to the child is no greater than that of pleasure to the parent. The coordinated instinctive responses of the young begin in many of the precocious birds, like the great herring gull, before birth. The egg is starred and pipped, and the bill of the little bird is seen, and its call note heard, for several hours before the shell is cracked open. The

split may occur with a certain degree of uniformity in the direction of the minor axis of the egg, thus dividing it into two equal or unequal parts, and when the chick crawls out it leaves, besides the shell and its membrane, the allantois, and what looks like a residue of the albumen. The shells which now encumber the nest are carefully removed by some birds, and dropped, presumably at some distance away, while in others they are brushed aside, or crushed by the brooding bird and receive no further attention. This removal of the shells so common in the Passeres and other orders, must be attributed to the cleaning instinct, and I have noticed that in the cuckoo, which removes the shells of the first two or three young to hatch in succession, is apt to leave those of the last when the cleaning instinct is on the wane. The allantois is sometimes picked out of the shell and eaten, as has been seen in the case of the gull.