CLASSI#ICATION. 47 
The orders and classes of mollusca have already been referred 
to; those now in use are in most cases natural. 
It has been sometimes asserted that these groups are only 
scientific contrivances, and do not really exist in nature but 
this is a false as well as a degrading view of the matter. The 
labours of the most eminent systematists have been directed to 
the discovery of the subordinate value of the characters deriy- 
able from every part of the animal organisation ; and, as far as 
their information enabled them, they have made their systems 
expressive ‘‘of all the highest facts or generalisations in 
natural history.””—( Owen.) 
M. Milne Edwards has remarked, that the actual appearance 
of the animal kingdom is not like a well-regulated army, but 
like the starry heavens, over which constellations of various 
magnitude are scattered, with here and there a solitary star 
which cannot be included in any neighbouring group. 
This is exceedingly true; we cannot expect our systematic 
groups to have equal numerical values,* but they ought to be 
of equal structural importance; and they will thus possess a 
symmetry of order, which is superior to mere numerical regu- 
larity. 
All the most philosophic naturalists have entertained a belief 
that the development of animal forms has proceeded upon some 
regular plan, and have directed their researches to the discovery 
of that ‘‘reflection of the Divine mind.” Some have fancied 
that they have discovered it in a mystic number, and have ac- 
cordingly converted all the groups into fives.t We do not 
undervalue these speculations, yet we think it better to describe 
things so far only as we know them. 
Great difficulty has always been found in placing groups 
according to their affinities. This cannot be effected in—-the 
way in which we are compelled to describe them—a single 
series; for each group is related to ali the rest; and if we 
extend the representation of the affinities to very small groups, 
any arrangement on a plane surface would fail, for the 
affinities radiate in all directions, and the ‘‘ network’ to which 
Fabricius likened them, is as insufficient a comparison as the 
“chain” of older writers. 
* The numerical development of groups is versely proportional to the bulk of the 
tudividuals composing them.—( Waterhouse.) 
+ The quinarians make out five molluscous classes by excluding the tunrcata ; the 
same end would be attained in a more satisfactory manner by reducing the pteropods 
to the rank of an order, which might be placed next to the opistho-branchs. 
t The quinary arrangement of the molluscous classes reminds us of the eastern 
