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180 new activity might well rise, which, if fostered, would be of advantage to the general commonwealth. But let us consider the old ones. Terns, as we have seen, are vigorous in the defence of their eggs and young. They mob and attack any one—be it bird, beast, or man—who trespasses upon their breeding-grounds. If, therefore, only about half the colony were needed for the nurture of the young, and thus gradually came to be the equivalent of the workers amongst ants and bees, in the other half there would exist the elements of a soldier caste. Of these it would become at first the more special, and in time the exclusive business, to drive all enemies away from the ternery; and since efficiency in so important an office might well outweigh the otherwise ill effects of a loss of fertility in certain members of the commonwealth, the soldiers, both male and female, might, in the continuous prosecution of their task, come gradually to lose the sexual instinct, which, again, would allow the others to lay, with advantage, a greater number of eggs. I have mentioned the case of a dog making regular daily expeditions to a ternery, in order to feast upon the eggs; and if one dog could commit havoc like this, what might not some wild egg-eating species do, if not efficiently kept away? It is obvious that the eggs thus destroyed might amount to more in number than those by the loss of which they would be saved to the community; and, on the other hand, a caste whose sole task it was to guard the eggs and young might be competent to guard a greater number than