Therefore, we will move about and pursue our researches among the rocks
and under the loose stones. Well, we are rewarded with other specimens:
here are several neat little shells, with a lengthened spire, and
with a remarkably thickened lip. This is the little Thick-lipped
Dog-whelk,[5] a very common mollusk with us under such stones as these
at low water-mark. And here is another species of the same genus,
the Netted Dog-whelk,[6] which is a much larger shell, being nearly
twice as long as the former, and marked with close transverse furrows,
which, crossing the longitudinal ribs at right angles, give a peculiar
reticulate surface, on which the specific name is founded.
Comparing these shells with the _Trochus_, we see that they have a deep
notch cut in the front part, of which no sign appears in the latter;
and this mark, trivial as it may seem, is an important indication
of the habits of the animal. The inhabitants of all shells which
have this notch are carnivorous, while those with simple lips are
herbivorous. The _Trochus_ gnaws or rather rasps away the tender growth
of marine vegetation, or the fronds of the grown _Algæ_, with its
remarkable palate-ribbon, all studded with reversed points, of which
I may find another opportunity to speak. The Dog-whelk, on the other
hand, acts the part of a cannibal ogre, feeding on his simpler brethren
of the bivalve shells; storming their stony castles, in which they seem
so secure, by open violence.
Look at this old valve of a _Mactra_. Like hundreds more that you may
pick up at high water-mark, it is perforated by a tiny hole near the
hinge, so smooth and so perfectly circular, that you would suppose a
clever artisan had been at work drilling the massive stony shell with
his steel wimble. No such thing: the Dog-whelk has done it: this is the
breach which he so scientifically effected in the fortress; and hence
he sucked out the soft and juicy and savoury flesh of his miserable
victim.
In order to understand his plan of operations, let us put down our
captive, and see him crawl. He is not long before he begins to march,
on his broad oblong foot, which, as you observe, is cream-coloured,
elegantly splashed and speckled with dark-brown. But before he moves he
thrusts out a long cylindrical proboscis from the front of his head,
which he carries high aloft and waves to and fro; and this organ, we
see, fits into the deep notch in front of the shell. This proboscis is
his drilling-wimble.