Chap. V. 
CONCHOLOGY. 
469 
Of the Con 
ftituent 
Parts cf 
Shells* &:c 
83 
Other expe' 
riments of 
Reaumur. 
-not by intus-fufception , or a circulation through the 
body of the {hell itfelf. If this were the cafe, the pro- 
duction of new matter to fill up the breach made in 
; the fhell, would firft appear all round the edge of the 
opening, and forming a kind of callus, iimilar to 
what happens in the reproduction of bony matter in 
other animals, it would gradually extend till the whole 
breach is filled up. Eut, on the contrary, this matter 
firft appears on the body of the- animal from which it 
has exuded, and the whole extent of the opening is 
clofed at once by the fluid which has been direCtly fe- 
creted from the furface of the body. Nor can it be 
fuppofed, that the liquid has infenfibly exuded from 
the (hell, and .falling on the body of the animal, is 
there collefted in fufficient quantity for the formation 
of the new piece of {hell. This is fully demonftra- 
ted by the two following experiments of the fame na- 
toralift. 
Reaumur broke feveral {hells of fnails ; and, hav- 
ing made a very large hole about the middle of the 
{hell, and about an equal diflance between its fummit 
and opening, he introduced between the body of the 
animal and its {hell, through the hole, a piece of 
{kin which was extremely fine, but of a very clofe tex- 
ture. He glued this {kin to the internal furface of 
the (hell, fo that it {hut up accurately the artificial 
opening which he had made. It muft then be obvi- 
ous, that if the reproduction of the piece of fhell which 
was removed, depended on the excretion of a fluid 
from the fhell itfelf, and not on that which proceeds 
from the furface of the animal’s body, the new piece 
of fhell would be formed on the external furface of the 
piece of {kin which was introduced 5 and it is not pof- 
fible that it could be formed between the {kin and the 
body of the animal. But the contrary of this has al- 
ways happened. The new teftaceous matter is always 
depofited on the internal furface of the Ikin \ that is, 
on the fide which is in contact with the animal’s body 5 
and no matter whatever was depofited on the other 
furface. This experiment has been repeated by others, 
and has been invariably attended with the fame re- 
fult. 
The fecond experiment made by Reaumur is not 
lefs decifive than the firft. He took a number of 
fnails and broke the {hells, fo that he diminifhed the 
number of the turns of the fpire about 4 part. Hav- 
ing in this manner rendered the ftiell too fmall to cover 
the body entirely, they were nearly in the fame fitua- 
tion as when an increafe of the animal’s body requires 
an augmentation of the fhell. He then took a bit of 
{kin, as in the former experiment, fuffrciently large for 
the opening of the {hell, and introduced one of its 
edges between the body of the animal and the {hell, 
to the interior furface of which he glued it } after 
which having folded back the other extremity of the 
{kin on the external furface of the {hell, he glued it 
in like manner, fo that the whole external opening was 
completely covered with the {kin. The refults were 
exadMy the fame as before. The {hell grew’, the {kin 
remained in its place, and that part of it which was at- 
tached to the interior furface was fixed between the 
new piece and the old {hell, which confequently could 
not contribute to its formation. 
From thc.fe experiments, which may be eafily repeated, 
it appears that the increafe of (hells is owing to the feere- 
4 
tion of an earthy and vifeid animal matter, which is pre- Of the Con- 
pared in the body of the animal, and which is fucceftively p U ” ent f 
formed by layers from the interior part of the {hell to Shel!s 
the external furface. This formation is determined < J ■ ■ .< 
by the previous enlargement of the animal. The dif- 84 
ferent ftrata or layers of which (hells are compofed, o{ 
can be eafily demonftrated by expofing them to the ^ burning 
adlion of fire, and removing them before their firuc- 
ture is entirely deftroyed. By this procefs the animal 
matter is confirmed, and the earthy fubftance remains, 
exhibiting a laminated llruCture. The fame ftrufture 
may be demonftrated, as has been already cbferved, 
in detailing Mr Hatchett’s experiments, by immerfing 
a ftiell of the defcription of mother-of-pearl in a dilu- 
ted acid. The earthy matter in this cafe is diffolved 
by the acid, and the layers of animal matter which 
are interpofed, refilling the aCtion of the acid, remain 
unchanged, and lull retain the original figure of the 
ftiell. 85 
It is a neceffary confequence of the mode in which Turns of 
the fhells of fnails are increafed, that they cannot 
. enlarge in volume, but by the augmentation of the 
turns of the fpire, and that the length of each turn of 
the ftiell already formed remains always the fame. 
This may be eafily put to the teft of experiment, by 
reducing the fhell of a fnail which has reached its full 
fize to the fame number of turns with thofe of younger 
{hells of the fame fpecies. The two (hells do not then 
exhibit any other difference than in their tbicknefs \ - 
and it wmuid be the fame, by comparing the youngefi: 
(hells, thofe which have been juft feparated from the 
egg, with the firft turns of thofe of the fame fpecies 
which have been reduced by breaking them to an 
equal diameter. The number of turns or whirls of 
which the fpire of a {hell is compofed, increafes very 
confiderably the fize of the fhell in univalves, and one 
turn more or lefs makes a great difference in their vo 
lume. According to Reaumur, the diameter of each 
turn of the fpire is in the fnail nearly double that of 
the preceding one, and \ of that which follows ; but 
in many other (hells, both marine and river, the lafl: 
whirls of the fpire, compared with the preceding ones, , 
greatly exceed this proportion. In fome, the external 
opening is 1 2 times greater than the preceding one, 
and in others, it is not more than eight times. This 
depends entirely on the increafe of the animal’s body, 
and the proportion of that increafe. The growth of 
fome is lengthw ife, and in them the increafe of diame- 
ter is proportionally lefs ; while others increafe more in 
thicknefs than in lengths Thofe teftaceous animals 
which have only a few turns in the fpire of the (hell, 
are of this defcription. To the former belong fuch as 
have a greater number of turns in the fpire. 
Thofe who have adopted the opinion of Klein with The animal 
regard to the formation of (hells, have denied the fe- is detached 
paration of the animal from the {hell, which fucceffive- jj 0 ™ 
ly takes place near the tip in univalves. It is indeed m a f es 
on this circumftance of the connexion of the animal ' 5 
with the {hell, that the truth of this theory depends. 
According to it, the animal is attached to the internal 
furface of the tip of the (hell in univalves, and on this 
connexion depend the increafe of the ftiell and even 
the life- of the animal. But it is a certain faft, that 
the pofterior part of the body of the animal is entirely 
detached from the tip of the ftiell 
and this holds, 
not 
