"How much better than learning the names and characters of all the species is it to learn of the origin, relation, and mode of existence of all the natural productions with which we are surrounded. "_First Part: Progress in structure of living beings in proportion as circumstances favor them._ "When we give continued attention to the examination of the organization of different living beings, to that of different systems which this organization presents in each organic kingdom, finally to certain changes which are seen to be undergone in certain circumstances, we are convinced: "1. That the nature of organic movement is not only to develop the organization but also to multiply the organs and to fulfil the functions, and that at the outset this organic movement continually tends to restrict to functions special to certain parts the functions which were at first general--_i.e._, common to all parts of the body; "2. That the result of _nutrition_ is not only to supply to the developing organization what the organic movement tends to form, but besides, also by a forced inequality between the matters which are assimilated and those which are dissipated by losses, this function at a certain term of the duration of life causes a progressive deterioration of the organs, so that as a necessary consequence it inevitably causes death; "3. That the property of the movement of the fluids in the parts which contain them is to break out passages, places of deposit, and outlets; to there create canals and consequently different organs; to cause these canals, as well as the organs, to vary on account of the diversity both of the movements and of the nature of the fluids which give rise to them; finally to enlarge, elongate, to gradually divide and solidify [the walls of] these canals and these organs by the matters which form and incessantly separate the fluids which are there in movement, and one part of which is assimilated and added to the organs, while the other is rejected and cast out; "4. That the state of organization in each organism has been gradually acquired by the progress of the influences of the movement of fluids, and by those changes that these fluids have there continually undergone in their nature and their condition through the habitual succession of their losses and of their renewals; "5. That each organization and each form acquired by this course of things and by the circumstances which there have concurred, were preserved and transmitted successively by generation [heredity] until new modifications of these organizations and of these forms have been acquired by the same means and by new circumstances;