PUTTING aside the instinct which forces the parent to feed the young without external assistance, we come to those cases where the parent has to seek food which the offspring could not have found for itself, and often to prepare it for the use of the offspring. In the greater part of the world, the milk of various animals is the staple of food, not only for children, but adults; and the “milk diet,” as it is called, is strongly urged by many physicians of the present day. The Kafir tribes, for example, a wonderfully powerful race of men, live almost wholly on sour milk, mixed with maize flour, never eating such valuable animals as kine except on great occasions. Yet the natives of the Tonga Islands think that nothing can be more disgusting than for a human being to drink the milk of a cow. How the operation of milking is conducted we need not say, whether it be performed on the cow as with most nations, or the ass in case of need with ourselves, or the mare as with the Tartars, or the goat and sheep in various parts of the world. The milk of the sheep, by the way, is singularly rich and nourishing. Suffice it to say that the animals which are to be milked are kept for that purpose, and that the touch of the human hand, rightly applied, induces the animal to part with its milky stores. * * * * * IN Nature there is an exact parallel. It has long been known that some species of Ants are in the habit of acting in exactly the same manner as ourselves, in not only extracting a nutritious liquid from other insects, but watching and tending those which furnish their daily food just as a good dairyman watches and tends his cows. [Illustration: ANT AND APHIS.] [Illustration: MILKING COW.] The Ants, being insects, would naturally require insect cows, and such are to be found in the Aphides, of which mention has already been made. These insects are furnished with a pair of very small tubercles near the end of the abdomen, and from them flows that sweet liquid which is so familiar to us under the name of “honey-dew.” For centuries no one knew the source of the sweet honey-dew which attracted all the bees of the neighbourhood to the tree on whose leaves it was sprinkled, sometimes in patches, and sometimes coating them with a thin shining coat, as if varnished. At last it was discovered that the honey-dew is, in fact, the liquid exudations from these tubercles upon the backs of the aphides, and that the ants feed regularly upon it. Not only do they lick up the honey-dew that has fallen from the ants, but they milk them, so to speak, exactly as a dairymaid milks a cow. With their antennæ the ants pat and stroke the tubercles of the aphides, and in a few seconds a drop of pellucid liquid appears at the extremity. This is the honey-dew, and is at once lapped up by the ant, which proceeds from one aphis to another until it has obtained its fill of the sweet food.