CHAPTER III.
SPONGES.
To many persons the statement that we are going for a ramble among the rocks in quest of sponges will merely suggest the idea of wreckage, and they will suppose that we have had information that a vessel, part of whose cargo was Turkey sponges, has gone to grief on the rocks near, and that sponges are to be had for the trouble of picking them up. And should they venture to accompany you on so promising an expedition, they would certainly consider you demented as, having reached the rocks that are only uncovered at very low tides, you proceeded to point out the green and orange and brown and whity-yellow expanses that coat the vertical faces of the rocks. All these things to them bear no resemblance to the only sponges they know—the ones they use daily for purposes of ablution. You can show them something approaching nearer to their ideal, if you hunt among the thick stems of the shrubby weeds on the rock. There, encrusting a branch, is a yellowish-brown form with rough surface and large pores very much like those they know all about. And attached to various weeds are others of the shape, size, and colour of melon seeds, with porous surface and open end.
a. Hymeniacidon albescens;
b. Pachymatisma johnstoni;
c. Halichondria panicea;
d. Grantia coriacea;
e. Halichondria incrustans;
f. Leuconia nivea;
g. Leuconia gossei.
Your friend, though disappointed, maybe, that he is not to share in the salvage of some splendid bath sponges from the supposed wreck, cannot help feeling some interest in the extensive layers of colour on the rocks, some of it raised into conical hillocks, and suggesting a fairy plain thickly studded with volcanoes. You tell him that these are really aquatic volcanoes so-to-speak, and that if you could get a portion off the rock, you could exhibit the phenomenon to him at work in a shallow dish of sea-water. Thereupon he, thinking to be of service to you tears off a slice of the pale green, hillocky sponge (Halichondria panicea) and breaks it up hopelessly. However, we will turn his clumsiness to account and take a view of the interior thus violently exposed. We see that these crater-like openings are the outlets to tubular spaces running through the sponge, and from these passages smaller branches go off at right angles, whilst these and the larger openings are surrounded by tissues that are very like bread in consistence; and that is really only a way of explaining that they are spongy. Now the whole of the substance of these sponges, as you may see by microscopical examination, is composed of myriads of minute flint spicules, finer than the most delicate fragments of “spun glass,” and of beautiful forms. Some are simple rods, straight and curved; others forked at one end; some like a gribble; others what is known as quadriradiate in form.
Now in some species these spicules are not arranged in any order; they are merely jumbled together, and their remarkable forms make it easy for them to become entangled. When so entangled they form the skeleton of the sponge. Each sponge is a co-operative colony containing many thousands of members, and these are represented to our view, through my pocket lens, in the mass only, as a thin clear jelly investing the spicule-tangles, or rather the spicules are imbedded in the sarcode as this living matter is termed. If we were to chip off a thin flake of rock with its investing sponge intact, and place the whole in a glass vessel full of water, we could observe the movements which manifest its vitality. A little finely powdered indigo or other colouring matter should be dropped into the water near the specimen. On closely observing it would be seen that many of these minute granules were flowing towards the sponge, then that they entirely disappeared through the very fine openings in the surface. A little later these particles will reappear, not where they went in, but in a denser stream issuing from one of the craters, which are scientifically designated oscula to distinguish them from the minute pores.
If we dissect the sponge under a microscope, we shall find that from one of these oscula a broad passage runs through the centre of the mass, and from the walls of this the minute pores run off to the outer surface. This central cavity is invested by a living membrane which, when examined through a higher power of the microscope, is seen to consist of myriads of organisms closely packed together side by side, and each resembling a glass vase, spherical below, with a wide neck, and from its centre there issues a long antenna-like process. This is called the flagellum (Latin, a whip), because its office is to lash the water. These flask-like organs, with their flagella, present a wonderful likeness to some free infusoria known as collared monads, and over this likeness and all that it may or may not imply to the systematic naturalist much ink has been shed, and the sounds of controversial strife it engendered, though now faint, are still audible. Into that question we do not go.
The combined lashing of these little whips in unison sets a strong current of water flowing through the central passages and out at the oscula. To feed this stream, water flows in automatically through all the little pores, and brings with it the infusoria and other minute particles of life with which the sea is swarming. These come in contact with the lips of the flasks in the interior over which the living jelly of the sponge is steadily flowing. The infusoria flow with it and are carried away by the current to a little clear space (vacuole) in the lower part of the flask, where it is digested, and the refuse portions are thrust out to go in the general stream and be carried out through the oscula. Each of these cells may be taken therefore as a separate individual, enjoying home rule, yet taking part in general efforts for the whole sponge-community, for we find that by some strangely communicated understanding, all these cells cease lashing the water for a time as though resting (or digesting their food), and the craters cease to pour forth their streams. But then after a time activity is resumed, the craters belch forth again, and we know thereby that the flagella are in active operation down below, not merely capturing and digesting food, but also absorbing oxygen from the inflowing streams, whereby vital energy is maintained.
After the cells have become full grown, they split transversely or longitudinally, and so increase their number, which means that the size of the colony increases. But some of these divided portions develop into eggs, which after fertilization are swept out into the ocean by the outflowing current, and settling upon some rock become glued down and grow, gradually, by division and subdivision, producing a new colony. Such is a highly condensed account of the general phenomena of sponge life. There are variations upon it in the life-history of well-nigh every species; but this will suffice to give my reader a general idea of what sponges are. For the rest, he must go down among the rocks, and search out the various species of many forms, and endeavour to add to the general sums of knowledge by some fresh observations respecting British Sponges.
However startling the statement may sound, there is no lack either of specimens or species on the British coasts. Some of the most conventionally sponge-like of these must be sought by the dredge in deep waters, but our own hunting ground, the rocks that mark the shoreward-bounds of the laminarian zone, if carefully inspected at low spring tides, will afford more specimens in half an hour than we can exhaust the interest of in a week. That this is no mere figure of speech you will agree when I add that Dr. Bowerbank published a work in three volumes dealing only with British Sponges, and to these a supplementary posthumous volume, edited by Dr. Norman, has since been added.
Where the rocks rise high above the shore with their upper portions tilted towards the cliffs, we shall find several species incrusting the vertical or overhanging surfaces of these rocks, such as Halichondria incrustans, whose buff-coloured bread-like surface is diversified with slightly raised oscula. Its principal spicules are knobbed at one end, in which respect it differs from the similar Halichondria panicea which is peculiar in having only one type of spicules—a rounded rod, slightly curved or quite straight, but pointed at each end. Ellis called this species the Crumb-of-bread sponge, a name which is reflected in the scientific cognomen panicea. It is one of the most plentiful of the encrusting species, and may be readily known by the greenish-yellow or distinctly green colour of its extensive patches.
Not far from the Crumb-of-bread will in all probability be found the similar Sanguine sponge (Halichondria sanguinea), of a bright red colour. The conical elevations of the oscula in these species distinguish them readily from the plump, though narrow bands of Microciona carnosa, a plentiful species that creeps extensively between the other kinds, its pale red branches being very unequal in width, and alternately contracting and swelling out, joining and separating. This will be found figured in the lower left-hand corner of our illustration on page 29.
COMPRESSA.
CILIATA.
A very noticeable species on account of its neat compact shape will be found attached to various red seaweeds, with which its whitish colour contrasts well. It is a small oval, usually from a quarter to an inch in length, very flat, but yet hollow, with a large vent at the free and larger end. This is the Grantia compressa. Careful search among the indescribable medley of “unconsidered trifles” that crust the rocks beneath the shelter of the Fucus-growth, will reward us with a little spherical sponge with tubular oscula at the summit formed of spicules, and its general surface bristling with long spicules. This is the Grantia ciliata, looking like a little gooseberry.
There are many other forms, for which I must refer my readers to Dr. Bowerbank’s work, where also will be found descriptions and figures of many deep-water species, such as the more conventional sponge-like Chalina oculata, in branching masses nine or ten inches high.
There is, however, one other we must mention; the so-called Boring sponge (Cliona celata), which attacks various shells and stones. It is quite a common occurrence for the rambler along the shore to pick up the shell of some mollusk, and find it so tunnelled, the borings branching in every direction, that what would otherwise be as strong as stone is now as weak as poor strawboard, and will yield to very slight pressure or strain. On breaking such a shell across we get both cross and longitudinal sections of these tunnels and chambers, and find some of them to be lined with a dark brown filmy tissue, the remains of some past inhabitant; others contain portions of this Cliona sponge, living or dead; others again contain little bivalve shells that just fit the aperture, whilst yet another set exhibit clean walls that may not have had any animal inmate. Much controversy has raged over the question whether these excavations have been made by the sponge, or by some boring worm, and there have not been wanting as advocates of either view men whose authority on sponge matters is unquestioned. Where such doctors differ how shall humble observers venture to give a verdict? For my part, I cannot give my support to the contention that the sponge has bored the clean holes, hollows, and tubes that I have seen in the large numbers of attacked shells I have broken; neither am I prepared with an opinion as to the creature that did make them. I believe that on this matter, as on many others connected with natural history, we have much still to learn, and every student of Nature should have his eyes and his mind ever open to receive hints from Nature herself as to her methods. One of these days, some lonely wanderer by the margin of the wave will show us how simply this boring is accomplished, and we shall all wonder that we never thought of the possibility before. But whatever views or lack of views we may have upon the question, “who made the burrows?” there is no doubt that the sponge does exist in some of them, and its spicules embedded in the yellow sarcode are well worthy of minute observation.