It is a very unusual occurrence for a man to take up a new subject after he is fifty years of age, and to become a master in it. But Lamarck did this. It is true that his previous training as a botanist had prepared him, and it is also true that his years of solitude and poverty had given him a singularly placid and meditative mind, and this was strengthened by his natural courage. Had Lamarck been a descriptive zoologist only, he would have been great; but the very method which made him great originated in some remarkable speculations which had hardly been expressed, seriously, by any man before. Not only did he place the animal kingdom with the lowest first, but he considered the will, instinct, and apparent reason of animals, and classified them accordingly with those which are apathetic, sensible, and intelligent. The idea of lowness of organization or of structure and lowness of nervous power amongst the simplest animals struck him to be of primary importance. Hitherto, quite as many people believed that the highest and most intelligent animals were created first, and that the lower ones had degenerated from them. Lamarck conceived that nature, acting by law, commenced with the simplest things, and that one species formed others, so that the present animals and plants are the outcome of those of the past history of the earth. He believed in incessant change in nature, and that when our knowledge is complete the apparently well separated and defined species will be found to be united by intermediate forms, and cease to be species. Hitherto naturalists had considered kinds of animals and plants, or species as they are more properly called, to have been specially created as they are seen by us, and that they were unalterable and invariable. No one with any great knowledge of animals and plants had speculated about the origin of species, and the causes of the differences of kinds, or had endeavoured to place all the great classes of the animal kingdom in a series, maintaining that they were related by descent. Right or wrong in his speculations, Lamarck made an epoch in zoology, by writing on the philosophy of zoology, and dealing with the possible causes of the different kinds of animals. He considered that during all the geological ages, down to the present time, animals and plants had been exposed to great changes in their external conditions; changes of climate, and of physical geography had happened, and that whilst some species had become extinct many had been changed, little by little, into others. Lamarck, and M. Geoffrey St. Hilaire declared it to be their opinion that there had been an uninterrupted succession in the animal kingdom, effected by means of birth and offspring from parents, from the earliest ages of the world to the present day, and that the ancient animals, whose remains have been preserved in strata, however different, may nevertheless have been the ancestors of those now in being.