which may take place in many of the lower animals is astonishing. Thus the tails of lizards, if broken off, will grow again, and the limbs of newts will be reproduced, with their bones, muscles, blood-vessels, and nerves. Even the eye and the lower jaw have been seen to be reproduced in the last-named animals. If certain worms be cut in two, each half will become a perfect animal, the head producing a new tail, and the tail a new head; and a worm called a _nais_ has been cut into as many as twenty-five parts with a like result. But the most remarkable animal for its power of repairing injuries is the fresh-water hydra, almost any fragment of which will, under favorable circumstances, grow into a new and entire fresh animal. It is also a notorious and very noteworthy fact that, in both man and the lower animals, the processes of repair take place the more readily the younger the age of the injured individual may be. But these unconscious but practically teleological processes of repair, are often preceded by actions which everyone would call instinctive. [7] See Mr. Timothy Holmes’s _System of Surgery_, 3rd edit. vol. iii. p. 746. There is yet another class of organic vital actions to which I must advert, which are at once utterly unconscious, while the fact that they are directed to a distinct end is indisputable; in fact they are purposive in the very highest degree that any unconscious actions can be purposive. They are the actions of true reproduction, and they come before us naturally here, since a consideration of the process of remedial reproduction in the individual, naturally leads us on to the consideration _of the reproduction of the species itself_. In the cases of the frog and the butterfly, everyone knows that the creature which comes forth from the egg is very different from the parent. Animals, in fact, mostly attain their adult condition by passing through a series of development changes; only as a rule that series is not abruptly interrupted by plainly marked pauses, as it is in the frog and butterfly, and, therefore, such changes, instead of being obvious, are only to be detected with difficulty and through patient research. Almost every animal thus goes through a series of very remarkable changes during its individual process of development or, as it is called, during its “ontogeny.” This process, in its perfect unconsciousness, is like reflex action, but it is far more wonderful, since in the earliest stages even nerve-tissue is absent and has itself to be formed. In the accuracy of its direction towards a useful end, it is the very counterpart of the most developed instinct; nor, if the impulses by which adult individuals are led to seek and to perform those processes which give rise to the embryo, are to be called instinctive, is it easy to see how the analogical use of the term “instinctive” can be refused to that impulse by which each developing embryo is led to go through those processes which give rise to the adult.