7 
aquatic or water Snail, to be fituated at the 
bottom or bafis 64 of them, but they are not 
provided with any vifible mufcle to move them. 
Even the horns themfelves, which end in fharp 
points cc, are only weakly drawn in occafionally 
in order to become fhorter. 
In fome of thefe Snails, I faw with amaze- 
ment that there were two eyes, placed near 
each other on the right fide of the creature, 
each of which was provided with its own pro- 
per chryftalline humour. This, I think, is very 
remarkable, and ftrongly demonftrates the man- 
ner wherein the eyes may be multiplied in in- 
fects, as I fhall hereafter demonftrate, when I 
fhall treat of Bees. The nerves of the eyes in 
this water Snail are lefs vifible than in the 
common kinds; nor do they arife immediately, 
as is faid, from the brain, but from a little 
nerve which lies towards the fore parts of the 
head. In other refpects the eye itfelf does not 
differ from that of the covered Snail, only that it 
is bigger, and in a manner pear-fhaped, or like 
an onion. The chryftalline humour is likewife 
larger in this, however diftinguifhably lefs the 
little creature may be in itfelf. 
The opening d of the verge is very worthy of © 
confideration, and has divers mufcles, by which 
it is dilated and contratted. The Snail fome- 
times gathers this aperture into an oblong tube, 
and ftretches or protends it above the furface 
of the water, in order to draw in and expel 
the air.’ This may not only be feen but heard 
alfo, by the noife which the Snail makes in 
moving the water. Nay, bythe affiftance of 
this aperture, through which the air is con- 
veyed into the inmoft furface of the membrane 
of the verge, and into the cavity of the body 
itfelf, the Snail makes a beautiful figure {wim- 
ming in the water. 
This creature can likewife immerge or dive 
to the bottom of the water, if it compreffes 
the internal air. This is effected in the fame 
manner as when the air is comprefled ina glafs 
with water in it ;. for little perforated glafs glo- 
bules fwim at firft in the water, by the aflift- 
ance of the air contained in their cavity: all 
thefe little globules fubfide as foon as the {mall 
quantity of air contained in them is condented ; 
which happens by the common preflure of the 
air, that is above the water in the glafs; but 
they emerge or rife again to the furface, as 
foon as the finger or any thing that ftopt it, is 
removed from the mouth or orifice of the glafs. 
This is a pleafant experiment, and I have found 
it very true, according as it has been defcribed 
by Cornelius Confentinus, in his platonic circum- 
pulfion. 
In the fame manner does this Snail fometimes 
dive under water, and again fwim to the fur- 
face, by properly managing the quantity of air 
in its body in fuch a manner ; the latter, being 
as heavy as the water, it candifficultly be fup- 
ported on the furface, and is again deprefied to 
the bottom by the leaft compreflion of the in- 
ternal air. But when the Snail expels all the 
air out of its body, which it will do if it 
‘Tlie, “BEOk OIE. of NATUR EB: ot, 
be pricked with a fharp-pointed little needle, it 
will not then be able to {wim up to the furface 
of the water, but by creeping flowly. So that 
from hence it is probable this creature would 
die, if any thing like it fhould happen in dirty 
or miry ditches; fince, in that cafe, it could 
not reach the furface of the water, until after 
fome days, and would therefore be fuffocated 
for want of refpiration. 
There is likewife a great difference, with 
refpect to the external skins or coats of the ge- 
nital organs; all the parts of generation in the 
covered Snail iflue out of one opening only, 
whereas in this aquatic or water Snail; all thofe 
parts and the entrances or mouths of each are 
diftinct. The penis indeed rolls out and erects 
itfelf from the neck through a peculiar aper- 
ture. Tab. IX. fig. rv. e. But the opening of 
the vulva is difpofed, by the wife Architect, im- 
mediately under the tube of the verge f. The 
verge itfelf likewife differs greatly from that of the 
common Snail; it is fmaller, more hollow, and 
capable of greater motion; but then it is fitted 
on the infide to every part of the extremity of 
the fhell eg, in the fame manner as it is in the 
common Snail. ‘The tooth 4, and little tongue 
which is feen under it, are of the fame tex- 
ture in this as in the common Snail; unlefs that 
the tooth it more equal, and not divided into 
fo many confiderable notches. 
The internal parts likewife differ much both 
in colour and ftru€ture: but the greateft diffe- 
rence is in the ftomach, which is membranous 
in the covered and other Snails, as it is in men 
and in quadrupedes; but in this water Snail it 
is of the fame ftructure in all refpects with that 
of the Hen-or Cock kind; fo that one would 
think the real ftomach of a Hen is here repre- 
fented, without any difference, but that it is 
much fmaller. Moreover, the colour of the 
craw or crop isa dark or obfcure gray. The 
gullet of this paffes likewife the chink or cre- 
vice of the brain, which is a very agreeable 
fight in this admirable creature. For fince the 
{wellings or productions of the {pinal marrow, 
are, by the addition of a certain heterogeneous 
yellow matter, here diftinguifhed, all thefe 
parts are therefore the more diftin@ly vifible. 
Hence it is, that one may, with greater eafe 
and certainty, eftablifh the anatomy of the 
water Snail, than that of the covered Snail ; for 
in the former are many coloured parts, by 
means whereof the mufcles, and many other 
parts, efpecially thofe of the palate and mouth, 
may be eafily diftinguifhed. 
The falival veffels of this are like thofe of the 
common Snail. ‘The liver is likewife com- 
pofed of vifible glandules, and rolled into the 
like fpirals. The heart alfo, with its pericar- 
dium, is placed in the fame order. The veffels 
on the verge, on the contrary, are not fo di- 
ftintly vifible. The lime bag is of a pale _ 
orange colour. All the mufcles are inferted in» 
the outer part of the fhell and its pillar. 
The organs of generation likewife differ: the 
penis in this water Snail is very broad; it is 
11s 
LIKE 
