ey." This group contains within it the large subordinate
groups, "paper money" and "metallic money;" the latter group again
contains the more subordinate and smaller groups, "gold money," "silver
money," and "copper money," and these respectively contain still more
subordinate and smaller groups. Thus, the group "silver money" contains
the subordinate groups--(1) crowns, (2) half-crowns, (3) florins, (4)
shillings, (5) sixpences, &c.; and any one of these (_e.g._, shillings)
is further divisible into groups of "shillings" of the coinage of
different reigns.

Reversing the process we may, as another illustration, select the group
of articles of furniture called "chairs," which (with other
_co-ordinate_ groups, such as "tables" and "sofas") is contained within,
and is subordinate to, the larger group of objects, "wooden furniture."
This latter and larger group is again classifiable (together with its
co-ordinate group, "metal furniture") in the yet higher and larger group
of "furniture made of hard material," to which the wooden and metal
groups are both subordinate. Co-ordinate with the group of "hard
material" we have another group (carpets, curtains, &c.) of "furniture
of soft material," and these two groups are again subordinate to the
largest group of all "furniture."

It was also pointed out in the introductory Essay[5] that there are two
kinds of classification, one artificial, the other natural--the latter
(the kind aimed at in this Essay) being such a system of classification
as leads to the association together in groups, of creatures which are
_really_ alike and which will be found to present a greater and greater
number of common characters the more thoroughly they are examined.

The system of classification which zoologists and botanists adopt is a
system founded upon the form, structure, number, and relations of the
parts of which each living being consists. It is, therefore, a
morphological system, and rests rather upon the appearances of parts and
organs than upon the offices which such parts and organs fulfil. It
rests, that is to say upon their forms, not upon their functions.

The mode in which animals have been arranged in zoological grouping
affords an exceptionally good model for classification generally, as has
been noted by the late John Stuart Mill.[6] In fact, the number of
subordinate groups is very great in zoology. Thus, the kingdom of
animals is subdivided into a certain number of very lar