they are collected into the paleal cavity, a
sort of petticoat over the piston, little
vibratile hairs push them up the interior of
the gill-siphon, anil from thence the sudden
distension of the piston ejects them in the
form of little oblong nodules.

The only difficulty which remains, in
regard to this species at least, is the first
introduction of the pholade into the rock.
When the growth of stones was an established
doctrine in science, the savans classed
the pholades with the frogs occasionally found
alive in blocks of marble. The discovery a
century ago of pholades in the pillars of the
temple of Serapis, at Naples, destroyed this
notion. Ever since, the question has been a
puzzle and a mystery. Since eighteen
hundred and fifty-one, the problem has been;
solved with scientific certainty. The gelatinous
egg-clusters, or spat of the pholades,
is thrown upon the rocks by the female.
After a day or two, the eggs separate and
become larves, and each chooses a convenient
site for his habitation. When the site is
chosen and the shell is strong enough, the
pholade, barely visible to the naked eye—a
creature the size of a big pin's head—fastens
his foot upon the rock, and the rasping,
squirting, and hydraulic machines begin the
work of life.

No doubt the explanations which are
satisfactory in regard to the dactyle pholades
cannot be received in regard to the spherical
pholades. Wonderful differences of structure
like these must entail corresponding
modifications of the perforating machinery.

The pholade zone is inhabited by the
mussels. The zones, I submit to elder and
better naturalists, ought to be characterised
zoologically by fixed animals, as they are
botanically by fixed plants. For want of
this guiding rule, animals have been ascribed
to particular zones, which wander over all.
In the brown laminarian, or pholade zone,
multitudinous colonies of mussels may be
seen moored to the breaker-lashed brows of
rocks. The presence of the plant-eating
conchylions is accounted for by the botanical.
and of the animal-eating, by the zoological
features of the zone. The white whelk, the
imperial purpura, lords it over the subject
populations of the mussel banks. Naturalists
say the mussels prefer the exposed brows of
the rocks because they love the shock and
dash of the breakers. The mussels have a
better reason. The bluffest points are the
only habitats where they can escape the
augur-like tongues of the white whelks.
Clothed in the white of innocence, the
purpura lurk among the roots of the tangles
and sea-girdles, watching for opportunities
of piercing the shells and sucking the blood
of the mussel colonies. Shelled oligarchs of
the shore, the white whelks wish to enjoy as
much prey and encounter as few breakers as
possible. Hence, the mussel colonies can
thrive only on rock-ledges where the purpura
are afraid to venture. To do them justice,
the white whelks chamfer or drill the holes
in the shells of their victims very beautifully;
the mussels, however, have the bad
taste to dislike it, and get out of the way of
it. It is in this way life goes on in the pholade
zone. There are egg-clusters in elegant and
tiny urns attached to stones, and there are
egg-clusters in gelatinous splatches upon the
brows of rocks. These are the destroyers
and the destroyed in the condition studied
by embryology. There are armed and adult
conchylions prowling in search of victims,
and there are defenceless and adult
conchylions braving the billows maddened by
the blasts, to escape their enemies. These
are the destroyers and the destroyed in the
condition studied by conchyliology. It is
with animals as it is with men. When the
student of topography searches into the
reason why cities have grown up in particular
sites, he generally finds the causes
which determined the choice of the site were
proximity to food and security from enemies.
Reasons similarly instinctive determine the
habitats of the spray acorns, the wrack
shrimps, the tangle winkles, and the breaker-
lashed mussels. The principle salus populi
reigns wherever there is life.

I never could find out how long the
pholades live, and whether they die, or are
cut off by shocking accidents. The holes of
dead pholades are full of sand. The entrances
of the holes become the favourite abodes of
the heart-like shells, cockles or cardiaceæ.
When the shells of the pholades are taken
out of their holes, the dingy blue colour of
the living shells has vanished, and they have
become singularly fragile and beautifully
white. All dead shells, indeed, found on the
shore are perfectly white and clean. Shell-
fish which have died in my possession have
quite another appearance; and the difference
is due, I suspect, to the voracious activity of
the flat-worms.

I have seen heart-shells, or cardiaceæ, of
the Venus kind, take up their abodes in the
mouths of the holes of the pholades. Venus
is nearly round or oval, and her bombed
shells fit in neatly into the mouths of the
holes. She possesses the powers of
locomotion in a very limited degree. If a man
were to lose both his legs, and to have his
left arm cut off, he would have to drag
himself about by means of his right arm. The
locomotion of Venus is similar. The animal
or goddess stretches out her foot or arm, and
when it adheres to the rock or sand, drags
her shell after it. When she finds a hole
she sweeps out the sand, scrapes the edge of
the hole a little to fix her lower valve, and
spins a gelatinous cable to moor herself
within it more securely. Now she is
comfortable, and feeding is henceforth her chief
business. She lies with her upper valve
raised, and the water brings her food to her
siphons. When she is hungry she makes