CLASSIFICATION. 45 
resemble the simpler orders of their own sub-kingdom, but not 
those of any other group. 
These are the yiews of Professor Owen—the successor of 
Hunter—by whom it has been most clearly shown and stead- 
fastly maintained, that the ‘‘ unity of organisation”’ manifested 
by the animal world results from the design of a Supreme In- 
telligence, and cannot be ascribed to the operation of a mechani- 
eal ‘‘ law.” 
CLASSIFICATION. 
The objects of classification are, first, the convenient and in- 
telligible arrangement of the species;* and, secondly, to afford 
a summary, or condensed exposition, of all that is known re- 
specting their structure and relations. 
In studying the shell-fish we find resemblances of two kinds. 
First, agreements of structure, form, and habits; and, secondly, 
resemblances of form and habits without agreement of struc- 
ture. The first are termed relations of affinity ; the second, of 
analogy. 
A finities may be near, or remote. There is some amount of 
affinity common to all animals; but, like relationships amongst 
men, they are recognised only when tolerably close. Resem- 
blances of structure which subsist from a very early age are 
presumed to imply original relationship ; they have been termed 
genetic (or histological), and are of the highest importance. Those 
which are superinduced at a later period are of less consequence. 
Analogies. Modifications relating only to peculiar habits are 
called adaptive; or teleological, from their relation to final 
causes.t A second class of analogical resomblances are purely 
external and illusive; they have been termed mimetic (Strick- 
land), and, by their frequency, almost justify the notion that a 
certain set of forms and colours are repeated, or represented in 
every class and family. In all artificial arrangements, these 
mimetic resemblances have led to the association of widely dif-. 
ferent animals in the same groups.{ Particular forms are also 
represented geographically§ and geologically,|| as well as sys- 
tematically. 
* At least 20,000 recent, and 16,000 fossil species of molluscous animals are known. 
{ For example, the paper nautilus, from its resemblance to carinaria, was long sup- 
posed to be the shell of a nucleobranch, parasitically occupied by the “ ocythoé.” 
f e. g. Aporrhais with strombus, and ancylus with patella. 
§ Monoceros imbricatum and buccinum antarcticum take the place, in South 
America, of our common whelk and purple, and solen gladiolus and solen americanus 
of our solen siliqua and ensis. 
| The frequent recurrence of similar species in successive strata may lead beginners 
to attribute too much to the influence of time and external circumstances; but suck 
impressions digappear with further experience. 
