98 
NATURAL HISTORY. 
[n. ZOOL. GAL, 
1. The great variations in size, the difference of surface and solidity, 
and the variations in external form produced by the developement or 
non-developement of the different processes in the individuals of the 
same species, all circumstances dependent on the quantity of food and 
the idnd of locality they inhabit. 
2. The change that takes place in the form of the shell during the 
growth of the animal, as the expansion of the lip of the Strombidce and 
the Cerithice , the contraction and inflection of the lips of the Cyprceidoe , 
and the developement of the varices of the Muricidce. 
3. A series of sections of shells to shew the form of the cavity, the form 
of the plaits, and the contraction of the size of the cavity of the shell to 
adapt it to the moving forward of the body of the animal, by the de¬ 
position of the glassy coat on the upper part of the whorls, or the de¬ 
position of cross septa separating the upper part of the cavity from the 
rest of the shell, which is most perfectly developed in the Chambered 
shell, or Nautili . 
4. Specimen shewing the manner in which the animals mend any 
accident to their shell. 
5. Specimen exhibiting the manner in which Mollusca remove by 
absorption certain parts of the shell which are no longer necessary to 
them, or may be in the way of their growth, and of the holes which they 
make in shells, rocks, or wood, to form habitations for themselves and 
to procure their food. 
6. The specimens exhibiting the manner in which the tubular shells 
are rolled up into a spire, beginning with the nearly straight JDentalium , 
gradually passing by the irregularly twisted Vermetus and the separate 
whorled Scalaria, to the common spiral shell; others, shewing the 
gradations of form in the involute and spiral shell; and lastly, some de¬ 
formed specimens exhibiting the same variations in different individuals 
of the same species of Mollusca, and the monstrosities which occur in 
the form of shells. 
7. Specimens shewing the manner in which Mollusca cover with a 
shelly coat any extraneous body which may become attached to their 
shells. 
In Cases 5 and 6 are a series of plaster casts of the interior of the 
different shells of living Mollusca, to facilitate the determination of the 
easts of the fossil species, which are so commonly found in the Portland 
stone and other geological formations ; at the same time these moulds 
are useful as shewing the form of the mantle of the different species of 
Mollusca, which is so liable to be distorted or contracted in the pre¬ 
served specimens, and exhibiting how 7 completely the shell is moulded 
on the body. 
In Cases 7 and 8 are placed a series of models on an enlarged scale, 
and some specimens of minute bodies. The nature of the animals w hich 
form them is not know n; and they may belong to several different 
orders. Some have supposed them to be internal shells; but this can¬ 
not be the case w'ith all, as many are attached by their outer surface to 
sea-weeds and shells. From their being formed of numerous chambers, 
they have been generally- associated with the Nautili , but they differ 
essentially from the latter in their construction, which consists of a 
number of cells piled one on the other; and in having no terminal 
cavity for the reception of the body of the animaL The cells are fur- 
