78 GASTEROPODA. 
This deposition of mucous, and of mucous mixed 
with calcareous matter, goes on as the animal grows 
and feels the want of a larger shell for its protec- 
tion. The shell is, in fact, moulded on the body of 
the animal itself, as the body grows; and, for this 
reason, any irregularity in the body is moulded in 
the shell. 
“The animal has the faculty, also, of mending 
any break or injury that its shell may have re- 
ceived, if it is not of such a magnitude as to de- 
range all the functions of the animal itself; and it 
mends them in the same manner as it forms its 
shell,—that is to say, by depositing first a coat of 
animal matter, and then lining it with mucous 
matter, mixed with chalk, to harden it. But as 
the animal is usually very desirous of getting the 
repairs done as quickly as possible, and is most 
probably damaged by the injury it has received, 
these repairs are generally much more roughly ex- 
ecuted than the shell itself, and commonly destitute 
of regular colour. 
“The particles, which vary the colour of the sur- 
face of the shell, are deposited while the shell is 
being increased in size, immediately under the 
outer mucous coat; and as these particles are also 
secreted by peculiar glands, the colour is always 
situated in a particular manner on each species, 
the glands being gradually enlarged, and gradually 
separated, but not changed in position by the 
erowth of the shell. All the variations exhibited 
in the colouring of the different species, or in the 
different individuals of the same species, are pro- 
duced by the permanent or temporary interruption 
of the action of these glands.’”* 
* Land and'Fresh-water Shells, 73. 
