"Moreover, if a single fact shows that an animal for a long time under domestication differs from the wild form from which it has descended, and if in such a species in domesticity we find a great difference in conformation between the individuals submitted to such habits and those restricted to different habits, then it will be certain that the first conclusion does not conform to the laws of nature, and that, on the contrary, the second is perfectly in accord with them. "Everything combines then to prove my assertion--namely, that it is not the form, either of the body or of its parts, which gives rise to habits, and to the mode of life among animals; but that it is on the contrary the habits, the manner of living, and all the other influencing circumstances which have, after a time, constituted the form of the body and of the parts of animals. With the new forms, new faculties have been acquired, and gradually nature has come to form the animals as we actually see them. "Can there be in natural history a consideration more important, and to which we should give more attention, than that which I have just stated? "We will end this first part with the principles and the exposition of the natural classification of animals." In the fourth chapter of the third part (vol. ii. pp. 276-301) Lamarck treats of the internal feelings of certain animals, which provoke wants (_besoins_). This is the subject which has elicited so much adverse criticism and ridicule, and has in many cases led to the wholesale rejection of all of Lamarck's views. It is generally assumed or stated by Lamarck's critics, who evidently did not read his book carefully, that while he claimed that the plants were evolved by the direct action of the physical factors, that in the case of all the animals the process was indirect. But this is not correct. He evidently, as we shall see, places the lowest animals, those without (or what he supposed to be without) a nervous system, in the same category as the plants. He distinctly states at the outset that only certain animals and man are endowed with this singular faculty, "which consists in being able to experience _internal emotions_ which provoke the wants and different external or internal causes, and which give birth to the power which enables them to perform different actions." "The nervous fluid," he says, "can, then, undergo movements in certain parts of its mass, as well as in every part at once; moreover, it is these latter movements which constitute the _general movements_ (_ébranlements_) of this fluid, and which we now proceed to consider. "The general movements of the nervous fluid are of two kinds; namely, "1. Partial movements (_ébranlements_), which finally become general and end in a reaction. It is the movements of this sort which produce feeling. We have treated of them in the third chapter.