ieee 
th Ha oP au yY of IN 68 eT s. 65 
As to the method, whereby fucha fhell is 
increafed, the following are the chief particu- 
Jars, the Snail’s whole body is furnifhed with 
glands, from the orifices of which flows up a 
kind of mucus or thick matter, like fmall and 
fine rays ; which, like fo many threads of filk 
or velvet, are joined together in one common 
cruft or iurface, and in procefs of time are 
condenfed, and acquire the hardnefs which we 
obferve in the fhell. This mucus or thick 
humour then, is the firft matter which grows 
into a membrane, and afterwards into a ftony 
skin. Its filaments are very confpicuous at the 
places where the windings of the {hell are ap- 
plied to each other. 
The outward fcale or enamel of the teeth, 
in-men as well as in beafts, likewife confifts 
of innumerable very fmall and very fine fila- 
ments joined together, which I have found in 
fome teeth hard and polifhed, like real ftone; 
though the teeth are at firft but a kind of mu- 
cus or thick humour, and afterwards become 
membranous, and at length fully hard. I have 
feen the rudiments of teeth in abortions of five 
months old, which, together with their fila- 
ments, I now keep, and can fhew in them this 
fingular conftruction. 
My moft refpected friend, Mr. Stenon, has 
likewife difcovered {uch filaments in oyfter- 
fells, and made my father a prefent, for his 
mufeum, ofa fhell which was buried for a long 
feries of years under ground, in the mountains 
of Italy, and, by length of time and moitfture, 
infenfibly had feparated, as it were, into many 
tender and {mall fhells: from this it is evident, 
that the fhell itfelf was formed of thofe, in its 
growth, in the manner I have explained. In 
corals I have found nearly the fame method of 
accretion ; that is, that they are firft thin mem- 
branes, which, by an infenfible increafe of the 
little grains joined together, petrify ; as may be 
feen in a work publifhed by Mr. Boccone, of 
corals, in which are two letters of mine treat- 
ing of the fame matter. 
If you likewife view the tendons of the 
Snail’s mufcles, which are inferted in this part 
of the fhell, you will find that they have grown 
hard as a ftone there; which is indeed eafily 
known, hyth from the winding of the thell’s 
pillar, which becomes larger by degrees, and 
from the infertion of thofe mufcles in the thell. 
In hens likewife, and in peacocks, the tendons 
of the mufcles are offified, or become by de- 
grees hard as bones. Thefe tendons, efpecially 
{uch as are taken out of the lower parts of the 
foot, are made ufe of, by fome with us, for 
toothpicks. 
The opercula of the thells, Tab. IV. fig. rir. 
m, havealmoft the fame origin, though their fub- 
ftance approaches nearer to chalk or platter 
than toa {tone ; nor is it fo hard, but is more 
fpungy than the fhell, and therefore is made 
thicker; but I have obferved, that when the 
operculum or cover is finifhed, and the creature 
enters deeper into the fhell, it afterwards, under 
the membrane of the fhell’s operculum, pro- 
duces, fometimes two, fometimes three mem-= 
branes, of which fome are thicker than others, 
and are more or lefs calcarious. About the 
center of this operculum, is likewife feen a 
membranous filament, which connects 2}! thofe 
membranes with the operculum, as if they 
were faftened with a needle and thread. When 
the creature frames its operculum or cover, it 
retires by degrees more and more into the hell, 
fo that the verge equally fhuts up its whole 
cavity, and afterwards preffes out the chalky 
moifture, with the affiftance probably of the 
facculus calcarius, or calcarious bag which we 
have defcribed. . 
The principal part of the body that promotes 
the increafe of the fhell, is that verge of the 
Snail, which the creeping in of the Snail caufes 
to {well fo far beyond the extremity of its little 
habitation, as that creature wants to ftretch and 
enlarge it, thus it prefles by degrees a gluti- 
nous humour out of the glands of the body, 
and thereof immediately forms a membrane 
confifting of filaments, which it afterwards 
makes thicker and thicker, until it at length 
attains a due hardnefs and firmness, by the 
preflure of the circumambient air. For this 
membrane is at firft fo weak and foft, that it 
breaks through on the flighteft-touch ; and this 
is the reafon why the halictations of Snails are 
found fo often uneven with fears, and {wellings 
on their furfaces. 
If it fhould happen that the fhell be prefied 
in by a fall, or by, any other means, or be 
wounded or broken, thefe Snails know {0 well 
how to.mend and confolidate it by degrees, by 
the application of the petrifying humour, that 
it becomes more firm than it was before in the 
places which fuffered the injury. The out- 
ward furface by this becomes very unequal 
and tuberous, but the inward fmooth and 
polithed. Something-like this is alfo obferved 
in the fractured bones of animals, which na- 
ture can confolidate again with a callous fub- 
ftance ; but even thofe are then alfo unequal 
on the furface after fetting. We fometimes 
meet with ribs of mutton in the fame manner, 
which it is very certain have been formerly 
fractured. I have feen the fame thing in dif- 
ferent bones of men and other animals. I have 
fometimes broke a Snail’s thell fo that I could 
put my little finger in the hole that I made, 
which, notwithftanding, I have found filled 
up again in four days : fo that the fame means 
of accretion and tran{mutation, to all intents 
and purpofes, are obferved in the Snail’s fhell 
asin the bones of other animals, with this 
only difference, that the veffels of the former 
are not confpicuous ; which may probably be 
owing to their fmallnefs and delicacy, and be- 
caufe the blood contained in them is white: 
but this makes no difference. 
Another thing alfo very worthy of greater 
admiration is, that this fhell will, even under 
water, whether it be frefh or falt, petrify or be- 
come hard as a ftone, howevermuch it has been 
like a fluid humour in the beginning. This 
) ; may 
