MOLLUSCA. a 
as united, and forming continuous crusts or ridges. These 
hairs, as well as the cuticle, are liable to be worn off, and 
in some places can seldom be perceived, unless in early 
age. 
The most important appendix to the skin, for such it 
must be considered, appears to be the shell. This part is 
easily preserved, exhibits fine forms and beautiful colours, 
and has long occupied the attention of the conchologist. 
The matter of the shell is secreted by the corium, and the 
form which it assumes is regulated by the body of the ani- 
mal. It is coeval with the existence of the animal, and 
appears previous to the exclusion from the egg; nor can it 
be dispensed with during the continuance of existence. 
The solid matter of the shell consists of carbonate of lime, 
united with asmall portion of animal matter, resembling 
coagulated albumen. 
The mouth of the shell is extended by the application of 
fresh layers of the shelly matter to the margin, and its thick- 
ness is increased by a coating on the inner surface. These 
statements are abundantly confirmed by the observations of 
Reaumur, (Mémoires de l’ Académie des Sciences, 1709), 
whose accurate experiments have greatly contributed to the 
elucidation of conchology. If a hole be made in the shell 
of a snail, and a piece of skin so glued to the inner margin 
as to cover the opening, the shelly matter will not ooze out 
from the broken margin of the fracture, and cover the out- 
side of the skin, but will form a coating on its inner sur- 
face, thus proving it to have exuded from the body of the 
animal. When a portion of the mouth of the shell of a 
snail is broken off, and a piece of skin glued to the inner 
margin, reflected outwardly, and fixed on the body of the 
shell, the defective part is again supplied, and the matter 
