p. 56
Chapter V


    The aim of a general arrangement of animals is not only to possess a convenient list for consulting, but it is more particularly to have an order in that list which represents as nearly as possible the actual order followed by nature in the production of animals; an order conspicuously indicated by the affinities which she has set between them.

    The aim of  a classification of animals, on the other hand, is to furnish points of rest for our imagination, by means of lines of demarcation drawn at intervals in the general series; so that we may be able more easily to identify each race already discovered, to grasp its affinities with other known animals, and to place newly discovered species in their proper position.  This device makes up for our shortcomings, facilitates our studies and our knowledge, and is absolutely necessary for us; but I have already shown that it is a produce of artifice, and that despite appearances it corresponds to nothing real in nature.


    In the animal kingdom such a principle is that every class should comprise animals distinguished by a special system of organisation.  The strict execution of this principle is quite easy, and attended only with minor inconveniences.

    In short, although nature does not pass abruptly from one system of organisation to another, it is possible to draw boundaries between each system, in such a way that there is only a small number of animals near those boundaries and admitting of doubt as to their true class.



    Man is condemned to exhaust all possible errors when he examines any set of facts before he recognises the truth.  Thus it has been denied that the productions of nature in each kingdom of living bodies can really be arranged in a true series according to their affinities; and that there exists any scale in the general arrangement either of animals or plants

    Naturalists, for instance, have noticed that many species, certain genera and even some families appear to a certain extent isolated
in their characters; and several have imagined that the affinities among living beings may be represented something after the manner of the different points of a compass.  They regard the small well-marked series, called natural families, as being arranged in the form of a reticulation.  This idea, which some modern writers think sublime, is clearly a mistake, and certain to be dispelled when we have a deeper and wider knowledge of organisation; and especially when the distinction is recognised between what is due to the greater or less progress in the complexity or perfection of organisation.

    Meanwhile, I shall show that nature, by giving existence in the course of long periods of time to all the animals and plants, has really formed a true scale in each of these kingdoms as regards the increasing complexity of organisation; but that the gradations in this scale, which we are bound to recognise when we deal with objects according to their natural affinities, are only perceptible in the main groups of the general series, and not in the species or even in the genera.