"From what has been said, we cannot doubt but that the inner and general feeling which urges the animals possessing a nervous system fitted for feeling should be susceptible of being aroused by the causes which affect it; moreover, these causes are always the need both of satisfying hunger, of escaping dangers, of avoiding pain, of seeking pleasure, or that which is agreeable to the individual, etc. "The emotions of the inner feeling can only be recognized by man, who alone pays attention to them, but he only perceives those which are strong, which excite his whole being, such as a view from a precipice, a tragic scene, etc." Lamarck then divides the emotions into physical and moral, the latter arising from our ideas, thoughts--in short, our intellectual acts--in the account of which we need not follow him. In the succeeding chapter (V.) the author dilates on the force which causes actions in animals. "We know," he says "that plants can satisfy their needs without moving, since they find their food in the environing _milieux_. But it is not the same with animals, which are obliged to move about to procure their sustenance. Moreover, most of them have other wants to satisfy, which require other kinds of movements and acts." This matter is discussed in the author's often leisurely and prolix way, with more or less repetition, which we will condense. The lowest animals--those destitute of a nervous system--move in response to a stimulus from without. Nature has gradually created the different organs of animals, varying the structure and situation of these organs according to circumstances, and has progressively improved their powers. She has begun by borrowing from without, so to speak--from the environment--the _productive force_, both of organic movements and those of the external parts. "She has thus transported this force [the result of heat, electricity, and perhaps others (p. 307)] into the animal itself, and, finally, in the most perfect animals she has placed a great part of this force at their disposal, as I will soon show." This force incessantly introduced into the lowest animals sets in motion the visible fluids of the body and excites the irritability of their contained parts, giving rise to different contractile movements which we observe; hence the appearance of an irresistible propensity (_penchant_) which constrains them to execute those movements which by their continuity or their repetition give rise to habits. The most imperfect animals, such as the _Infusoria_, especially the monads, are nourished by absorption and by "an internal inhibition of absorbed matters." "They have," he says, "no power of seeking their food, they have not even the power of recognizing it, but they absorb it because it comes in contact with every side of them (_avec tous les points de leur individu_), and because the water in which they live furnishes it to them in sufficient abundance."