Let us come back from the wide world of waters, with its nightly
illuminations, and its other ten thousand marvels, to our own homely
and quiet beach. A tribe of existences is awaiting our notice, which we
have as yet neglected; which yet we cannot fail to observe whenever we
peep beneath these boulders, and look at these rocky ledges, just left
exposed by the lowest retiring tides. They are the Sponges; the most
debateable forms of life, long denied a right to stand in the animal
ranks at all, and even still admitted there doubtingly and grudgingly
by some excellent naturalists. Yet such they certainly are, established
beyond reasonable controversy as true and proper examples of animal
life, and therefore having a rightful claim to be painted and
described in this series of essays. However, as they are the lowest, so
shall they be the last; for, with a few notes on some of our species,
I shall dismiss my kind and courteous readers.
The inferior surface of this huge slab of limestone, supported at
one end by a boulder, while the other end is imbedded in the mud or
concealed by the smaller fragments that are thrown in confusion around,
is densely studded with organisms. It is only at very low tides that
this arch is exposed, though now we can creep in and work with no great
discomfort, though with some defilement of our garments from the mud
and slime. The absence of direct light is favourable to the growth
of marine productions, and thus we have another congenial element in
the obscurity. With some of the smaller sea-weeds, chiefly of the
filamentous kinds, as _Cladophora_, _Conferva_, some of the minuter
_Callithamnia_, etc., the majority of the forms that crowd and cover
the rock so densely are animals: indeed there are large areas where
the animate forms struggle so perseveringly for standing-room, that
not a filament or frond of vegetation can be seen, and you could not
thrust the point of a penknife down to the rock in any spot without
wounding some or other of the incrusting creatures. _Polyzoa_ are
here, chiefly of the tufted species; _Hydrozoa_, too, hang down;
Anemones, but not in abundance, may be seen; _Saxicavæ_ push their
crimson siphons through, here and there; _Botrylli_ are spread in
patches, and _Amœrœcia_ are suspended like a plentiful crop of tempting
strawberries; but Sponges constitute the staple of the crop; it is a
veritable field of Sponge.
I have on other occasions described some of the more characteristic
phenomena of this class of creatures;--the volcanic eruptions of the
Crumb-of-bread Sponge, the hills and poles and webs of the Rosy Crumb,
the protrusile bladders of the Sanguine, the starry spicula of the
Flat-Sack.[157] These I shall assume as known, and shall confine myself
to the enumeration and description of a few other species which are
found congregated on this rocky roof.
One of the first to catch the eye, by its gorgeous colour, is a rather
thin, soft, spreading patch, of the richest vermilion hue.[158] It is
of close substance, the surface covered with shallow irregular sinuous
channels and minute orifices. It rarely exceeds an inch in diameter,
but throws out slender clinging processes to some length. The flesh is
dense. Under the microscope it contains three-rayed spicula, which are
for the most part somewhat blunt, but some are very sharp. After death
it rapidly loses its brilliant hue, and dries of a dull oak-brown.
Another occurs in the form of low irregular spreading patches of a
greyish black, very smooth and shiny, more plump than the former, and a
little larger.[159] There are no visible orifices on the surface. The
substance is yellowish grey, compact, with a distinct demarcation from
the thin black tough skin. The spicula of the flesh have three rays in
one plane, and one standing up from it; very stout, sharp-pointed, with
a distinct canal running through the centre of each ray of the larger
ones. There are a few rods abruptly hooked at the tip; a few very long,
straight, and slender, with pin-like heads; and a few simple needles,
long, slender, pointed at one or at both ends.
Some largish rounded masses occur, several inches in diameter, and
rising to a thickness of three-fourths of an inch.[160] The surface
is undulate, the summits slightly ridged, covered with shallow
sinuous channels having sharp edges, not very confluent: large round
mouth-orifices (_oscula_) generally mark the summits of the ridges.
The colour of this fine species is a deep buff, and its appearance is
much like that of our Turkey Sponge, with something of the same feel,
but much firmer. The interior is full of channels. The spicula here
are very varied and interesting, comprising some curious and unusual
forms. Some, indeed, are simple needles, nearly straight, pointed at
one end rather abruptly. The following are minute. There are a number
of rings interrupted at one side, like the letter C, some thicker and
more elliptical, others slender and rounder, C. A few take the form of
the letter S, but having one lobe much more developed than the other.
Some of the C form have both the extremities bifid, and the points
widely diverging; and some of these have the back straight, instead of
curved, and these with their bifid points, look, when viewed in front,
like double anchors. All are, as usual, spun out of the most brilliant
glass.
Then we have in some abundance a sort[161] with firm cartilaginous
walls, about one-eighth of an inch thick, standing up to the height of
three-fourths, with rounded summits, running in irregular sinuations
and convolutions, not unlike the cartilage of the human ear, enclosing
deep hollows. The colour is opaque white, tinged with red, probably
from the red mud, which is prevalent here. When cut with a knife this
sponge has a sharp, crisp, gritty feel, and when a little is crushed
between glass plates we distinctly hear a creaking sound. These
phenomena depend on the circumstance that it is almost wholly composed
of great stout three-rayed spicula, solid throughout, together with a
multitude of excessively slender needles, straight, long, pointed at
one end; and many others as slender, but very short; no longer, indeed,
than the thickness of one of the three-rayed.[162]
Equally numerous with these, and possessing a certain amount of
resemblance to them, are some thick, compact, sack-shaped masses,
with angular edges and blunt points: sometimes they are flattened and
dilated, like a sack when empty; sometimes rounded, like a sack when
full. In the former condition several perforations occur along the
terminal ridge, in the latter there is generally but one. The colour
is white, slightly tinted, just as in the preceding. It stands up
boldly and stiffly (or rather _hangs_ in the natural state) from its
rather narrow base to the height of about two-thirds of an inch, and
the flattened specimens are as wide as this. It is nearly made up of
three-rayed spicula, some of large size, but more rather small. A
transverse section shows no obvious arrangement, except that of the
great central channel, into which the points of the spicula project;
but a longitudinal section shows the spicula built up one on another
in many courses, so nearly symmetrical that hexagonal canals are
formed, whose axes run transversely to the axis of the sponge; _i.e._,
horizontally. There is very little fleshy or gelatinous matter.[163]
Again we see a showy species,[164] making soft, spongy patches of an
orange or red-lead colour, an inch or more in diameter, rising into
ridges a quarter of an inch high, and forming low peaks, whose apices
are perforate. Its substance contains simple needles, long, nearly or
quite straight, pointed at one end; these are found in great numbers
in close array, the points mostly projecting from the surface. Some of
them are twice as thick as others.
Now we notice another peculiar form:[165] creeping, worm-like masses
of orange-yellow or buff hue, soft and spongy in texture, which throw
up one or more free, erect processes, irregularly curved, an inch or
more long, and about one-eighth thick on an average, but frequently
swollen and contracted by turns. These are not tubular, and the tips
are rounded. The general surface under a magnifier appears slightly
channelled. Within we find simple needles, long, nearly straight,
pointed at both ends, moderately numerous, enveloped in much yellow
granular flesh.
Then there are some imposing masses of a globose form,[166] some
of which attain a foot or more in diameter, though others are not
more than an inch. The surface is compact and smooth, of a delicate
purplish-grey hue, with a few minute orifices, each surrounded by a
small paler area.
The spicula in this noble species are various: simple rods, straight,
thick, long, slightly spindle-shaped, blunt at both ends, with a linear
axis; three-rayed, large, stout, very unequal angled, without any
central channel; a number of very small five- and six-rayed stars, the
rays projecting in different planes. They are set in a dense, yellow,
gelatinous flesh, in which we may at all times discover many gemmules,
or eggs; the smaller (or younger) are nearly round, bristling with
points in all directions like sea-urchins, changing as they grow larger
to a more oval form, beset with rounded warts, instead of points. These
are discharged, when mature, with the currents of water, through the
orifices, and find their way to some suitable spot, where they develop
themselves into the parent form.
Finally, here is a sort[167] whose colour is a pale Indian red;
occurring in masses which take the form of thick, plump bands, about
half-an-inch in width, but alternately swelling and contracting, which
creep over the rock, meeting and uniting, and then separating, so as to
leave hollow open interstices, which, however, in some specimens are
gradually filled up. The swellings form pointed hillocks, the apices of
which are pierced with from one to three orifices. Irregular shallow
channels cover the hillocks, and converge to the apices. It contains
simple needles, slender, straight (or slightly curved), pointed at each
end, not very numerous, thickly invested with granular flesh. This
Sponge shrivels much, and becomes shapeless in drying, but changes
little in colour. It is abundant.[168]
[Illustration: