If from these general considerations we enter in detail into Lamarck’s theory, we find room for the objections with which the opponents of the system of variety are engrossed, with which they have made those weapons of ridicule which act so well on minds which are not forewarned, and who are ignorant of this master’s _whole system_ of ideas. The grandeur of Lamarck’s views, the majestic simplicity of his theory, ought to be sufficient to shield him from such attacks. He saw at the beginning organic matter grouping itself under simple forms. These first outlines, altered by time and circumstances, have successively given birth to radiated creatures, to the inferior molluscs, the articulate animals, then the lowest fishes, then man. Here is a mistake, in our opinion; if there exists (until we know more) an immense and impassable difference somewhere in the animal kingdom, it is between the vertebrate and the invertebrate animals. Whilst the first show an admirable unity of organic composition, the second do not seem to have any at all, so that they do not admit of serial or linear classification. Each of the groups which they form is united by some particularity to all the other groups, and naturalists have even been able to differ about what must be considered as the highest round in the animal ladder. The organism of the invertebrata possesses a flexibility and immense variety, which is almost a characteristic special to these beings in which the nervous system ceases to present the profound unity which we see in the vertebrata; whilst the entire group has only a negative characteristic, _the want of vertebræ_, which is sufficient alone to show how unnatural it is. As for the rest, the vertebrate animal, even at the first moment of his embryo life, is absolutely irreducible to any invertebrate type whatsoever, contrary to Lamarck’s opinion. A vertebrate is to an invertebrate as two first numbers are to one another; all the vertebrata, on the contrary, are one to another as a simple number raised to different powers; they can all be brought back to their origin, and both the most complicated and the most elevated of the series are only the most simple ones arrived at a state of considerable perfection.