SNAIL. 
5 87 
pleases. The young snail, when first excluded from 
the egg, is completely formed, with a shell upon 
its back of a minuteness proportionable to that of 
the body, and of the dimensions of the egg which 
enclosed it. The first shell is extremely thin, and 
proves the basis of a second, which is perpetually 
increasing; and the little shell, such as it is at its 
eruption from the egg, will always be the centre of 
the other, which the animal, advanced in her growth, 
forms and completes by adding new circles to the 
first shell : and as her body can only be extended 
towards the aperture, this must consequently be the 
part that receives the fresh accessions, the materials 
of which are lodged in the body of the animal, and 
formed by a liquor or viscous fluid of considerable 
tenacity. This glutinous secretion is transmitted 
through a great number of little channels, to the 
pores with which the whole surface of the body is 
perforated, and thickens into a consistence round 
the mouth of the shell. It is here drawn out into a 
thin film, under which a second is soon after extend- 
ed, and this proves a covering to a third. From the 
union of these three films results an incrustation of 
the same quality with the rest of the shell. When 
the animal increases in bulk, and the extremity of 
its body is not sufficiently covered, it continues 
to secrete the materials, and build in the same 
manner. By these means it erects and repairs its 
habitation . 
To prove that this secretion is constantly used for 
the purpose above mentioned, several snails were 
