In the training of animals (and young children) artificial associations, pleasurable or painful, have to be established in connection with certain actions. Abnormal appetences and aversions have to be introduced into the mental constitution. In this process much depends on the plasticity of the constitution. In the absence of such plasticity it is impossible to establish new associations. We have seen that words are arbitrary[GH] symbols, which we associate with objects, or qualities, or actions. Can animals, we may ask, form such arbitrary associations? There can be little question that they can. Many of the higher animals understand perfectly some of _our_ words. The word "cat" or "rats" will suggest a construct to the dog on which he may take very vigorous action. How far they are able to communicate with each other is a somewhat doubtful matter. But the signs by which such communication is effected are probably far less arbitrary. And, in any case, the communication would seem to refer only to the here and the now. A dog may be able to suggest to his companion the fact that he has descried a worriable cat; but can a dog tell his neighbour of the delightful worry he enjoyed the day before yesterday? I imagine that what a dog can suggest to his neighbour is what we symbolize by the simple expression "Come." But I am fully aware that other observers will interpret the facts in a different way. Here is an anecdote that is communicated to me by Mr. Robert Hall Warren, of Bristol. "My grandfather," he says, "a merchant of this city, or, as Thomas Poole, of Stowey, would have preferred calling him, 'a tradesman,' had two dogs, one a small one and another larger, who, being fierce, rejoiced in the appropriate name of Boxer. On one of his business journeys into Cornwall he took the smaller dog with him, and for some reason left it at an inn in Devonshire, promising to call for him on his return from Cornwall. When he did so, the landlord apologized for the absence of the dog, and said that, some time after my grandfather left, the little dog fought with the landlord's dog, and came off much the worse for the fight. He then disappeared, and some time afterwards returned with another and larger dog, who set upon his enemy, and, I think, killed him. Then the two dogs walked off, and were no more seen. From the description given, my grandfather had no doubt that the larger dog was Boxer, and, on returning home, found that the little dog had come back, and that both dogs had gone away, and, after a time, had returned home, where he found them." Now, some will say that the little dog told Boxer all about it; but I am inclined to believe that the facts may be explained by the communication "Come."