VS 
THE GEELONG NATURALIST. in 
SHELLS—AND WHAT THEY TEACH. 
Bx Mr. J. F. Mur»rR. 
Tue study of shells and their inhabitants is one of the most 
interesting that can can be pursued by a lover of natural history. 
If he confine himself to their external appearance, and compare: 
them with the other orders of creation, with reference to the beauties. 
the shells alone present to the eye, he will find that they are inferior 
to none in form or colour; exhibiting the most exquifite contours, 
with the most varied and beautiful tints. If he pursue his examin- 
ation further, and, without limiting himself to the exterior, fix his: 
attention upon the living animal as well as the inanimate shell in 
which it resides and which it eonstruets for itself, he will be amply 
repaid by the search. ,He will find the same harmony existing in- 
all its relations, the same adaption of means to the end required, 
the same fitness of the creature for the element in which it is to 
reside, and the mode of life it is to pursue, as he will trace in the- 
more complieated and apparently more perfect animals. 
The mollusea have a soft body, most of them being entirely 
destitute of bones, though some are provided with internal shells, 
more or less perfectly formed. To compensate for the apparent 
deficieney 1n this respect, and to enable them to provide themselves 
with a defence against injury to which they might be liable from so: 
delicate a structure, they have been furnished with an external skin 
or envelope covering them more or less completely, and from 
which a liquid exudes, which on exposure to the air or water, 
hardeus into shell. Thus most of them are enabled to cover them- 
selves with a secure, and at the same time commodious and beautiful 
habitation, into which they can retire by the aid of strong contractile 
muscles far enough to escape from danger when it approaches. 
4 
This outer skin is now usually called the mantle, and is common to: ' 
most species of mollusea. 
As a considerable portion of these animals live entirely in the- 
water, from which they derive their nutriment, and which they 
breathe by the aid of bronchis, resembling the gills of fish, it is 
necessary that means should be provided for the admission of that 
fluid to the interior of the body; and, in order to effect this, certain: 
openings occur in the mantle, through which the water passes and 
returns, and by which also the head and foot, when these parts. 
exist, are put forth and drawn back at the will of the animal. In 
univalves this mantle is in the form of a sac, and has an opening in. 
front. ' In bivalves it is divided into two lobes, one for each valve. 
