S H E 
edges- with it's little teeth. It fometimes devours 
thofe fragments J at others, it only cleans away the 
margin when covered with films, and then adds 
^another rim to it's abode. 
The maniifafture of the Shell is natural to the 
fnail^ and without it the inclofcd aniinal could 
not long exift. For tliis purpofe, it's whole body 
is furniftied with glands, from the orifices of 
which exfudes a kind of flimy fluid, like the 
threads of fmall fpiders, which unite in one com- 
mon cruft or furface, and in time condenfe, and 
acquire a ftony hardnefG. It is this flimy humour 
rhat grows into a membrane, and afterwards a fl:ony 
fkin: nor can the gliflrening fubn:ance the fnail 
leaves behind it have efcaped the obfervation of 
the mofl: incurious ; this being in reality the matter 
with which the animal either augments it's Shell 
or repairs it's defeats . 
To explain the method in which the Shell is 
formed in a fl:iU more fatisfaflory manner. The 
fnail burfl;s from it's egg with it's Shell on it's 
back: this Shell, though very fimple, is the cen- 
tre round which every fucceeding convolution is 
formed, by new circles added to the former.' As 
the body of the fnail can be extended only to- 
wards the aperture, the mouth of the Shell alone 
can receive augmentation. The fubft^ance of 
which the Shell is compofed is chiefly fupplied 
by the animal itfelf; and is no more than a flimy 
fluid which gradually indurates. This fluid pafies 
through an infinite number of minute glands, 
till at lengch it arrives at the pores of the fl<:in; 
but there it is impeded by the Shell which covers 
the part below, and therefore is protruded to- 
wards the mouth, where alone it is necefl^ary : there 
the firft layer of flime foon hardens; and then 
another is added, which indurates alfo; till in 
time the Shell receives an adequate degree of 
ftrength for the prefervation of the animal. Thus 
every Shell may be confidered as a compofition 
of layers of flime, originally proceeding from the 
creature's own body. 
But though the formation of Shells is gene- 
rally accounted for in the foregoing manner, it 
has been fuppofed by fome, and with apparent 
reafon, that there are other fubfliances befidcsthe 
animal's own flime which afllfl: the fabric of the 
Shell, or at leaft: add to it's external coat, which 
IS always different from the internal one : thefe are 
accidental concretions of earthy or faline parti- 
cles, which adhere to the flimy matter on it's firfl: 
emifllon. By adopting this theory, v/e can more 
fatisfailorily account for the various colours of the 
Shell, which cannot be fuppofed to derive it's 
tindure from the animal's body, as is the vulgar 
opinion J for all the internal parts of the Shell are 
of ORe uniform white colour; and it is only the 
outermofl: layer that is fo beautifully varied, and 
fo richly tinftured with the mofl: vivid colours. 
If, as Argenville aflferts, the external coat be fcaled 
off, all the inner fubfl:ance will be found of one 
fimple colouring; confequently, the animal's own 
juices can afford only one colour; whereas we fre- 
quently fee Shells ftained with an infinite variety. 
If we examine the cabinets of the curious, we 
jhall find the Shells in general furniflied with a 
■white ground, tinftured with red, yellow, brown, 
green, and feveral other fliades and pleafing mix- 
tures, but never blue. Indeed, Shells are of al- 
mofl: every tinge but blue; the reafon of which is 
obvious, that being the only colour which fea~wa- 
t«-r annihilates. A piece of filk, or a feather of 
SHE 
this colour, on being put into an infufion of fait, 
urine, or nitre, lofes it's tint entirely. And may 
not this furnifh us with an idea of the operations 
of Nature in the colouring of her Shells ? that, in 
order to produce colour, the animal not only fur- 
nifhes it's iuices, but the fea ortlie earth that com- 
mixture of fubftance which is to unite with them. 
Neither the animal flime alone, nor the external 
earthy or faline fubflrances individuallv, could 
produce colours; but both united yield'an effe6b 
which neither fingly poffeffed. Thus Shells af- 
fume every colour but blue; and that, as pre- 
vioufly remarked, is defl:royed by fea-water. 
Hence therefore it appears that the animal alone 
does not tin6lure it's Shell; but that external 
caufes co-operate in contributing to it's beauty. 
It is probable that, from the nature of it's food, or 
other unknown circumfl:ances, the external layers 
of it's flime may be of different confiffences, fo 
as to affume various and beautiful hues whea " 
united with the particles of earth or fait acciden- 
tally incorporated with them from without. But 
the internal layers, which receive no adfcititious ad- 
mixture, ftill prefcrve the natural colour of the 
animal, and continue white without any varia- 
tion. 
Thus far we may difcover that the animal is 
not the fole agent in the beauty and colour of it's 
Shell. But it feems otherwife with regard to it's 
convolutions, it's prominences, and general form: 
thefe entirely depend on the art of the animal; or 
rather on it's inftinfts, which, in the fame kinds, 
nature has rendered invariable. The Shell gene- 
rally bears fome rude refemblance to the body on 
which it has been moulded. Thus it is obferv- 
able in all marine Shells, that if the creature has 
any tumour or excrefcence on- it's body, it occa- 
fions a prominence lilcewife in that part of the in- 
crufl:ation to which it correfponds. When the 
animal begins to alter it's polition, and to make 
new additions to it's apartments, the fame pro- 
tuberance which had raifed the Shell before in 
one part, fwells it again at fome little difl:ance; 
by which means we perceive the fame inequality, 
in a fpiral line, all round the Shell. Sometimes 
thefe tumours in the creature are fo large, or 
pointed, that thofe which rife over them in the in- 
crufl:ation appear like horns: after this, the ani- 
mal difengages itfelf from it's firfl: cavities; and 
then, by frefli evacuations, affumes a new fet of 
horns; and fo incrcafes the number in proportion 
to it's growth. If, on the other hand, the body- 
happens to be channelled, the Shell that covers it 
will be channelled likewife; and if there be any 
protuberances in the body, which wind about it in 
a fpiral manner, the Shell will likewife have it's 
tumours and cavities winding round to the extre- 
mity. 
In this manner the Shells are as various in their 
figures as the inclofed animals are different. In- 
deed, the divcrfity is fo great, and the figures and 
colours are fo very fl:riking, that feveral perfons 
have made the arrangement of them the ftudy and 
bufinefs of their lives. Thofe who confult their 
beauty only, take care to polifh them, and to have 
their external crufl or periofteum fcoured off by 
means of fpirits of fait. But others, with more 
learned affeflation, keep them exadlly in that 
fl:ate in which they were found, with their precious 
cruft ftill untouched. The expence which fome 
perfons have been at in making fuch colleftions 
is unbounded; and fome Shells arc no lefs va- 
luable 
