218 
NATURAL HISTORY. 
an oblong tube, and stretches or protends it above the sur- 
face of the water, in order to draw in or expel the air, as it 
finds occasion. This may not only be seen, but heard also 
by the noise which the snail makes in moving the water. By 
dilating this it rises ; by compressing it, the animal sinks to 
the bottom. 
But what renders these animals far more worthy of notice 
is, that they are viviparous, and bring forth their young not 
only alive, but with their shells upon their backs. This 
seems surprising ; yet it is incontestibly true : the young 
come to some degree of perfection in the womb of the 
parent ; there they receive their stony coat ; and thence are 
excluded, with a complete apparatus for subsistence. 
This striking difference between the fresh- water and the 
garden snail, obtains also in some of the sea kind ; among 
which there are some that are found viviparous, while others 
lay eggs in the usual manner. But this is not the only dif- 
ference between land and sea snails. Many of the latter en- 
tirely want horns; andnoneof them have above two. Indeed, 
if the horns of snails be furnished with eyes, and if, as some 
are willing to think, the length of the horn, like the tube of 
a telescope, assists vision, these animals, that chiefly reside 
in the gloomy bottom of the deep, can have no great occasion 
for them. Eyes would be unnecessary to creatures whose 
food is usually concealed in the darkest places ; and who, 
possessed of very little motion, are obliged to grope for what 
they subsist on. To such, eyes would rather be an obstruc- 
tion than an advantage ; and perhaps even those that live 
upon land are without them ! 
There is a difference also in the position of the mouth, in 
the garden and the water snail. In the former, the mouth is 
placed cross-wise, as in quadrupeds; furnished with jaw- 
bones, lips, and teeth. In most of the sea-snails, the mouth 
is placed longitudinally in the head ; and, in some, obliquely, 
or on one side. Others, of the trochus kind, have no 
mouth whatsoever ; but are furnished with a trunk, very 
long in some kinds, and shorter in others. 
Of all sea snails, that which is most frequently seen swim- 
ming upon the surface, and whose shell is the thinnest and 
most easily pierced, is the Nautilus. Whether, upon 
these occasions, it is employed in escaping its numerous 
enemies at the bottom, by seeking its food at the surface, we 
will not venture to decide. It seems most probable, that 
the former is the cause of its frequently appearing ; for, 
upon opening the stomach, it is found to contain chiefly 
that food which it finds at the bottom. 
