THE GEELONG NATURALIST. #7 ] 
by a kind of sliding motion. Those tribes which do not creep along: 
the ground, but move through the water, have recourse to various 
methods to enable them to swim; some float, borne as the winds 
and waves direct; a few can glide along the surface of the water, tho 
body and shell hanging down below, the foot alone retaining them 
in this position; others by squirting out suddenly a stream of water; 
which they have taken into their shells, send them forward in an. 
opposite direction; and others swim by using their foot as a fin and. 
. moving it from one side to the other. 
In those shell-fish which affix themselves permanently to a. 
submarine object, the method of attachment varies considerably. 
Some for instance, are fixed by a shell; some by a continuation of 
the foot either in a mass or divided into separate fibres; some by a 
tube; and others by a number of threads which they spin and fix. 
to different parts of the rock or other substance on which they dwell ; 
some excavate holes in soft rocks, and others in timber. In the 
locomotive mollusca the foot is often used for burrowing in the sand. 
or mud. 
With regard to food on which they live there is as much variety 
used as among animals of a higher class. Some are carnivorous, 
and some herbivorous. Some prefer living forms; others dead or 
putrescent. To meet these different forms of nutrition, varied and. 
diversified organs are required; and it will be found that these 
animals have apparatus well adapted for every case. Amongst 
those which are carnivorous some are furnished with appendages 
by which they can capture their prey, as the cephalopoda 
or cuttle-fish tribe; others that are fixed, by producing a slight 
current, obtain a constant stream of water supplied to their mouths,. 
bringing with it minute animals which they retain, as the oyster. 
The mouth of many is in the form of a proboscis (A), which is: 
long in mitra episcopalis, and is furnished with little hooks (2) with, 
which they can penetrate the shells of those they feed on, and extract 
the contents by drilling a little round hole, often seen on shells, the 
inhabitants of which are thus entirely destroyed by their enemy. 
Those which are herbivorous, or have no proboscis, cut their food by 
the aid of a tongue, which is rough with recurved spines and teeth.. 
This, as seen by the aid of a good microscope, is avery curious 
object, being formed like a ribbon, with a row of jagged teeth in the 
centre, and frequently three rows of hooks on each side. 
Mollusca produce their young from eggs, in the same way as fish. 
and birds. They are extremely prolific, and it is stated that the 
the mussels produce 300,000 young in one season, and the oyster: . 
not much less. Fortunately land shells are less prolific. 
