certainly have tamed the beautiful zebra and quagga; the elephant, brought by Hannibal over the Alps, fell back with Northern Africa into wildness. Only nutritive and formative augmentation of advantages which an animal may have acquired in the wild state could come into consideration here, and these would have to be hereditary to lead to perfection in a course of generations.
This seems, thirdly, not to come to pass. No matter for how many generations man cuts off the tail and ears of dogs, tail and ears return with each new brood. The mutilation which the Semitic races have performed on their children for hundreds of ages, and which Islam has imposed upon a great part of the population of the Old World, is not yet chronicled in nature. If, now, artificial defects are not hereditary, how may we venture to suppose that those artificially acquired changes which appear as favorable results of exercise are conveyed through egg and seed to posterity?
To this argument the following considerations are opposed: Although deformities produced by exterior force are not inheritable, we nevertheless see that incontestably internally acquired changes are only too surely transmitted. Of this, the host of hereditary diseases affords an example. Since cellular pathology has shown that the most various heritable diseases of the tissues, the most malignant as well as the most harmless forms, move within the limits of the once given type, the difference appears exposed to light which separates an artificial deformity from a retrogression caused by disease; and it becomes comprehensible why in tame rabbits, the tips of the ears of which may have been idle for many generations, the ear-muscles disappear, and the ears hang down limp; and why the eye and visory substance of subterranean and cave-inhabiting animals waste away. But, even if a deterioration within the type of the species by lack of exercise becomes hereditary, formations dependent on nutritive and formative stimulation, which also remain necessarily within the type of the species, may likewise be transmitted. This appears even to be the case with the inworking of the central nerve-system in certain forms of emotion, of which the growing wild of the at first confiding bird on a formerly uninhabited island furnishes a classical example. Certainly animals in freedom do not, like those under human training, become habituated to definite, frequently repeated functions, yet hunger and love, hatred, cold, thirst, etc., drive them likewise to the frequent performance of certain acts. So? finally, might the innate superiority called instinct (Kunsttrieb) have been gradually developed through practice, and the more easily, as a certain degree of pleasure is connected with the execution of series of movements that have become familiar. If, then, instinct does all that is necessary for the maintenance of the species, there is no more room for further improvement or for development in new directions, and the species remains at the stage it has reached as bees and spiders have done ever since man has known them. We may confidently assert that at
