On each side of the mouth there springs a lengthened horny thread,
appearing to answer to the antennæ which in other Worms, as well as
in Insects and Crustacea, project from the front of the head. Such
seems their true relation considered structurally, but in function
and office they are very remarkable and quite peculiar. To these
organs is assigned the duty of closing up the tube when the animal has
withdrawn its gaily-coloured plumes; and for this end, one of these
antennæ is much lengthened, and at the end is expanded into a broad
trumpet-shaped club, the extremity of which is somewhat concave, and is
delicately marked with radiating grooves. This organ is usually painted
with the same brilliant colours as the gill-tufts, and by its length,
size, and form, makes a very conspicuous feature in the charming
Serpula. Its length is such, that when the gill-filaments are rolled
up and withdrawn, the conical club enters after all, and is found
accurately to fit the trumpet-like orifice of the tube, just as a cork
fits tightly into the mouth of a bottle.
Ordinarily those organs which appear in pairs are formed so as to be
the counterparts of each other. But here is an exception. One only,
sometimes the right, sometimes the left, indifferently, takes the
remarkable form that I have been describing, the other being much
shorter, and terminating only in a small knob, like the head of a pin.
Why should there be this difference? Why this exception to an all but
universal rule? The reason is obvious. Yes, obvious enough when seen
and noticed; but it tells an eloquent tale of the Divine forethought
and care. If both of the antennæ were furnished with the terminal cone,
one would interfere with the other in the performance of their closing,
corking-up function; they would jam in the doorway, and the tube would
be left open. Hence the one is left undeveloped, yet retaining, as
I believe, the latent power of expanding into a cone, if it should
ever be needed by the accidental loss of the fellow now so furnished.
I thus judge, because experience shows me that the conical club is
occasionally thrown off, and quickly renewed, in captivity.
My esteemed friend, the Rev. Sir Christopher Lighton, has indeed put
on record an example of a Serpula of this species possessing two equal
antennæ, that had replaced the single one accidentally lost. They were
both perfectly developed, and joined together near the base. Each was
decidedly smaller than the single one that had formerly occupied their
place.[143] This exceedingly interesting case can, of course, only be
regarded as a monstrosity of redundancy, as children are sometimes born
with a superfluous finger. But it is valuable as showing that there is
a power of development latent in the crownless antenna. I wish very
much that the excellent observer had added a note, telling us to what
extent the tube was closed, and how the work was performed without
mutual interference.
It has been sometimes brought as an objection to our assigning a
certain service to certain organs, that the necessity for such service
is a gratuitous supposition, since other creatures similarly formed
in most respects, and in which we might infer a like need, have no
such supply. We may admit the facts, but refuse the reasoning. There
can be no manner of doubt that the conical antenna does act as a
stopper to the Serpula, as our eyes can see; and surely it would be
most unphilosophical to suppose that the function so performed is
not serviceable to the creature. Yet its near cousins, the Sabellæ,
similarly constructed, and of similar habits of life, and as we should
have _à priori_ supposed, quite as liable to injury in the same
direction, are entirely destitute of this contrivance for protection,
and of anything compensating for it, so far as is known. Why the need
of one should be met by such a beautiful contrivance, while the same
need in the other is wholly unmet, though both are formed by the same
Infinite God, is one of those unanswerable questions which, while they
leave unimpeached His wisdom, make us deeply conscious of our own
ignorance.
We find numerous examples of this genus _Sabella_ in our confused
heap of tangled life and death. By their vigour and their abundance
we have proof enough that their wants _are_ supplied, though they do
not enjoy this special contrivance: they manage to live and thrive
and enjoy themselves, with open doors, taking all risks of insidious
robbers,--such, for instance, as that vile burglar, the Longworm,[144]
that we found under a stone the other day; which is ever on the watch
to insert its snaky head within the unprotected tube, and to tear away
with merciless clutch the beauteous gill-tufts.
[Illustration: