MOLLUSCA. 
We have another objection to this artificial system, and Mollusca. 
one which we consider of great force; that, wherever it——\—= 
336 
Mollusca. belongs, and contentedly remains in this ignorance, he has 
=~ yet to learn the value of method in natural history. He 
cherishes with mistaken fondness the maxim of Linnzus, 
«« Nomina nosse oportet qui rem scire velit,” while he over- 
looks a more important object, expressed in the motto of 
the Linnzan Society, “ Naturze discere mores.” 
These remarks apply to the conchological labours of Lin- 
neus and his followers, who have devoted their whole at- 
tention to the arrangements of the shells, without attending 
to the animals. We kriow that some of the admirers of 
the Swedish naturalist presume to say, ‘ But our great au- 
thor was not wholly inattentive to the creatures for which 
the beautiful and endless diversified receptacles that he had 
characterised were designed. Among the generic marks 
was included the name of the molluscous inhabitant; or, 
where the animal differed from any which had a place in 
other parts of his system, he described it at length.” (Linn. 
Trans. vol. vii. 175.) Now, to what does all this attention 
of Linnzeus amount? In all the species which he has de- 
scribed, he has only noticed the animals of four of these, 
and in a very slight manner ; and, with regard to the name 
of the molluscous inhabitant which he included in his ge- 
neric marks, we hesitate not to say, that by this union he 
has betrayed carelessness. To many British ears these terms 
may sound harsh, but the proof of their correct: application 
in the present instance will be abundantly evident, if we 
examine the references to the animals of a few of his ge- 
nera. The genus chiton is thus characterised ; “ Animal 
Doris. Testz plures, longitudinaliter geste, dorso incum- 
bentes.” Are we not led to conclude from this character, 
that the animals of the chiton exactly resemble the animals 
of the doris genus, with the addition of the shells? If this 
be the case, how artificial is that system which places these 
two genera in separate orders! _ Upon turning, however, 
to the genus doris among his vermes mollusca, we find the 
foliowing characters assigned to it; “Corpus repens, ob- 
longum, subtus planum. Os antice subtus. Anus postice, 
supra cinctus ciliis. Tentacula duo, supra corpus antice 
intra foramina retractilia.”. Now, the fine fringes around 
the anus of the doris, which are the branchiz of the animal, 
and form the essential character of the genus, are not to be 
found in the animals of the chiton, whose branchiz are in 
the form of leaves placed along the margin of the body, and 
the anus is a simple pore. 
According to the generic character of the mya, the ani- 
mal is an ascidia, with the appendage of a shell. Upon 
turning to the genus ascidia, we find it said, “ Corpus fix- 
um, teretiusculum, vaginans. Apertura: bina, ad summi- 
tatem ; altera humiliore.” To prove the impropriety of re- 
ferring the animal of the mya to the genus ascidia, we shall 
only mention, that the former has a foot, and possesses a 
locométive power; the latter has no foot, remains immove- 
ably attached for life upon the substance to which it at first 
adhered, and depends on the accidental bounty of the waves 
for all its nourishment. 
The animals of nearly all the univalves are represented 
as belonging to the genus limax. But, with the exception 
of the restricted genus helix and bulimus, the animals of the 
univalves are all generically different from the limax. Their. 
tentacula are generally two in number, with the eyes at the 
base ; while the tentacula are four in the limax, with the 
eyes at the tips of the two longest. These examples will 
suffice to establish a truth so palpably obvious. 
The principal objection against this system of employing 
the shell, to the exclusion of the animal, arises from the 
fact, that nature has not drawn a line of distinction between 
the mollusca and the testacea. Thus, many of the vermes 
mollusca of Linnzus include shells in their bodies, as the 
aplysia ; and many of his vermes testacea likewise are soft 
on the outside, the shell being inclosed by the integuments, 
as the helex laevigata, now constituting the genus VELUTINA. 
prevails, the form and habits of the animal are overlooked. 
How fully is this truth illustrated in the works of the testa- 
ceologists of this country! We might examine all their 
writings, from the Pinax of Merret to the Descriptive Ca- 
talogue of Maton and Raket, including the works of Pen- 
nant, Berkenhout, Da Costa, and Donovan, and learn little 
more, besides the habitat, than that to every shell there is 
an animal attached. Of this charge the names of Lister 
and Montagu stand acquitted. The former has given us 
several good dissections; and the latter minute descriptions 
of the testaceous animals. 
Whilst, in the preceding remarks, we have objected to all 
arrangements taken exclusively from the characters of the 
shell, we also disapprove of those systems founded exclu- 
sively on the characters of the animal. By the former class 
of methodists, the simplicity of nature is sacrificed to their 
peculiar views, and, by the latter, practical utility is disre- 
garded. Devoting their whole attention to the animal, the 
later naturalists have overlooked the house in which it 
resides ; the roof which shelters it from the blast ; and the 
walls which guard it from its foes. The former obsery- 
ers possessed very limited views of nature, ‘and erected 
systems obviously artificial. To the systems of the latter, 
the same objections will apply. Thus, for example, among 
the univalves of Adanson, the families are formed from the 
position of the eyes chiefly. That the black points which 
we witness at the tips or at the base of the tentacula are 
actually eyes, we readily admit; but what influence have 
these eyes on the habits of the animal? or rather, does a 
change of position of these organs occasion a corresponding 
change in the habits of the animal? Unless thisisansweredin 
the affirmative, we must consider such characters as equally 
artificial with any employed by Linnzus or his followers, 
since they have no relation to any of the primary functions 
of life. 
The employment of characters taken exclusively from the 
animal is attended with so many practical difficulties, that 
it never can be introduced into general practice. If we find 
a shell thrown ashore, the animal may be dead, or it may re- 
fuse for a time to display its organs, and prevent us from 
arriving at its name and history. This defect, however, 
is partly remedied when we can call to our aid the charac- 
ters furnished by the shell. 
Another objection against this method arises from the well 
known difficulties attending the preservation of the soft parts 
of molluscous animals. To dry these, destroys their form and 
texture ; to inject them is impracticable; and when put 
into spirits of wine, they generally appear a shrivelled mass. - 
But the coverings of these animals are durable, and, since 
they form a part of the animal ; since they are produced at 
first along with it, increase by the addition of new matter 
from its body, and continue attached to it for life ; we must 
condemn any classification from which the shell is excluded. 
From these remarks, it will be obvious, that we consider 
the mixed system as the most natural and the most useful. 
It possesses all the advantages to which the other systems 
lay claim, while it is free from their defects. It withdraws 
part of our attention from the shell, because it is destitute 
of peculiar vessels, and possesses no vital energy, to fix it 
on those organs of the animal which are subservient to its 
existence. It leads us to examine the whole animal, instead 
of certain parts of it merely, and has a tendency to excite 
us to become acquainted with the manners of a tribe, from 
which, imperfect and artificial systems have hitherto with- 
drawn our attention. 
VALUE OF THE CHARACTERS EMPLOYED. 
It is of the utmost importance in the formation of any ar= 
rangement of natural bodies, to have an exact idea of the 
