Homes Without Hands: Being a Description of the Habitations of Animals, Classed According to Their Principle of Construction
There are many species of Astræa, all very pretty, and some quite beautiful. Among the most conspicuous are the ABNORMAL ASTRÆA (Astræa abdita), in which the mouth is scarlet and the tentacles yellow; the ANANA ASTRÆA (Astræa ananas), where the tentacles are yellow, but the mouth white; and the CHOCOLATE ASTRÆA (Astræa fusco-viridis), where the mouth is green, surrounded with a broad chocolate border, and the tentacles are white.
In the left centre of the illustration is seen a group of that most beautiful zoophyte which is known as the RED ORGAN-PIPE CORAL (Tubipora rubeola [or syringa]).
This handsome zoophyte is found chiefly off Carteret, in New Ireland, and is grouped together in masses that are often many yards in diameter. It is usually found in about two or three feet of water, but is sometimes placed so high that at very low tides it is laid bare by the receding waters.
The animal which forms this wonderful tubing is cylindrical, and the tentacles are pinkish, not possessing the brilliant red of the tubes, and in its native state the animals envelop so completely the upper part of the general mass that the bright red head is not perceptible. The coral masses are very fragile, and will not bear the pressure of the human foot, crumbling beneath the tread as if they were made of sugar. The tubes are beautifully cylindrical, and do not adhere to each other, being kept asunder by partitions, which precisely resemble the boards through which the pipes of an organ are passed.
They are very thin, though hard, and a rough pressure of the hand will always damage them. My own specimen is now sadly shorn of its original fair dimensions, at least half of its tubes having been broken away by the rude grasp of servants' hands, just as my best specimens of the paper nautilus and other fragile curiosities were damaged before I learned to put them under lock and key.
The animal is not a large one, its length being scarcely greater than that of the distance from one partition to another. The arrangement of the tubes and the partitions looks very complicated, but is, in fact, simple enough. The animal secretes around itself the calcareous substance which forms the tube, but when it has reached to its full extent, it is obliged to leave the cylindrical home in which it had resided. The partition is then secreted by the edge of the mantle, or membrane by which the creature is attached to its tube, and the zoophyte then begins another tube immediately above that which it has quitted.
Sometimes there is a kind of floor that separates the upper tube from the lower, but it is extremely thin, so that a tolerably stout bristle can be pushed through it. The partition is at least twice as strong as the tubes, which are scarcely thicker than the paper on which this account is printed, and is not solid, but perforated with holes just like the machine-made bricks which have lately come into use. In my own specimen there is a curious proof of the abundance of submarine animal life. The group of Organ-pipe Coral has enveloped a piece of White Coral, and has shown a remarkable instance of the manner in which beings so low in the scale of nature can accommodate themselves to circumstances. As if conscious that the coral formed an obstacle which they could not pass in a direct line, they ceased from tube-building when they arrived within a little distance of the coral, and threw up a partition vertically instead of horizontally, so as to envelop the greater part of the coral with the red calcareous substance. Having done so, they then made a new foundation upon the coral, and built a fresh series of tubes, so that, when viewed from above, the series of tubes is quite uninterrupted, and no one would imagine that any extraneous substance had intruded into the mass.
The tubes themselves have formed the basis of other submarine habitations, for a moderate magnifying-glass shows that sundry molluscs and molluscoids have settled down upon their exterior, while the white serpentine tubes which creep among the perpendicular pillars show that the serpulæ and other tube-making creatures have taken up their residence in so well-protected a spot.
AT the bottom of the sea there are a vast number of wonderful and interesting animals that are known to naturalists as Tubicolous Annelides, i. e., Tube-inhabiting Worms. These creatures are
Terebella Conchilega.
<!-- pandi-media-anchor:figure-p423-o67-09dd24e95ddabc7e -->Serpula Contortuplicata.
Sabella Unispira. Sabella Alveolaria.
true architects, not inhabiting the tubes which have been constructed by other creatures, but making them gradually, and in some instances getting together sand, stones, mud, shells, and other objects, which they use as materials for their homes. We may call the caddis grubs, which have recently been described, the tubicolous larvæ of fresh water, and very curious are the habitations which they construct. In salt water, however, there is much more variety than in ponds and rivers, and the tubicolæ are many and diversified.
We will begin with those which are most plentiful, and which are best known, because the hardness of their tubes causes them to be preserved long after the inhabitants have perished. If the reader should happen to have used a dredge, or a trawl, he must have brought to the surface great numbers of white shelly tubes, some of them being nearly triangular, and adhering by their whole length to a stone or a shell, and others nearly cylindrical, and rearing themselves from the stone after the first half inch or so. These are the work of a curious worm, called by Linnæus the SERPULA, on account of the serpentine manner in which its tube is formed. There are many species of Serpula, and some of the more conspicuous among them will be mentioned.
The Serpula belongs to the Annelidæ, or Ringed animals, a very large group, which includes the earth-worm, the leech, the nereis, and many other well-known creatures, all of which have the body composed of a great number of rings, and are destitute of true feet. They breathe either through the skin, by sacs, or by gills, and in the present genus the respiration is by means of gills, which are always delicate and elegant in form, and mostly brilliant in color. The body of the Serpula is comparatively short, the tube being frequently six or ten times as long as the animal which made it, and in consequence the Serpula possesses a deep and safe retreat, into which it can withdraw itself whenever threatened by danger.
The very fact, however, that the worm lives in a tube, causes the observer to ask himself how the creature contrives to breathe, and how the long tubular shell is kept clean. A reference to the illustration will explain the former of these difficulties, and the latter will presently be touched upon.
Projecting from the orifice of the shell may be seen a curious fan-like appendage; were the illustration to be colored, this fan would have been tinted with the brightest hues of scarlet and white, though no brush could give the wondrous delicacy of the feathering or express its semi-pellucid beauty. This "fan" is composed of the gills of the Serpula, and the animal is enabled to breathe by its power of projecting them from the orifice of its tube.
If the reader can procure a group of living Serpulæ and a little sea-water, he is strongly advised to do so, as he will understand their structure far better than can be the case if he merely refer to books. The creatures can be procured at any of the numerous shops in which aquaria are sold, and as they are plentiful on our own coast, they can be procured at a very cheap rate. They are terribly apt to die, unless the purity of the water be carefully preserved; but even in that case they can be dissected, and will afford lovely objects for the microscope. There is always an abundance of Serpulæ in the aquarium house at the Zoological Gardens, and the keeper is quite willing to give any advice as to the management of these interesting annelids.
Supposing, then, that a group of Serpulæ has been procured, it should be placed in the aquarium close to the glass, and, if possible, the vessel should be one with flat sides, the ordinary fish-globes giving a distorted image. A magnifying-glass should then be fixed so as to command the orifices of the tubes, and all will be ready. It is necessary to fix the glass, because the Serpulæ are strangely sensitive beings, and retreat into their tubes at the slightest alarm. If even a hand be moved suddenly, though at some little distance, the Serpulæ shoot back into their tubes as if propelled by springs, the feathery tentacles collapsing, and the beautiful operculum closing up the entrance.
This lightning-like rapidity of movement is caused by a wonderful array of hooks on the front portion of the body. These hooks are placed on the foot-warts which edge that part of the body, and are wonderfully adapted for catching the membrane that lines the tube. The botanist who looks at such a group as is now before me in the microscope would be instantly reminded of the seed-vessels of the "wait-a-bit" thorn, with its double array of hooked prickles. Each hook is rendered still more effective by the six or seven teeth into which its inner edge is cut, so that the most formidable array of hooks that the ingenuity of anglers ever devised, and named with appellatives as strange as their shapes, would appear quite harmless by the side of the Serpula's hooks, could they only be magnified to proportionate size. One bunch of these most formidable hooks would seem to be all-sufficient for the purpose, but when it is remembered that every foot-wart has its hooked armatures, amounting to fourteen or fifteen hundred in number, the power of the creature's hold ceases to be surprising.
Perhaps the reader may ask how the animal ever contrives to push itself out of the case at all, seeing that it is held by such a grasp. A farther look through the microscope shows that the hooks are affixed to long tendinous bands, of great delicacy, but at the same time of great strength, which enable the animal to protrude the hooks so as to seize the membrane, and to withdraw them when their purpose has been served. The dark background illumination shows the formation of the hooks in a very clear and beautiful manner.
If possible, the observer should preserve specimens of the hooks for the microscope. He will not want for examples, as the creatures have a habit of coming out of their tubes and dying on the floor of the aquarium, to the great discomfiture of the owner. I find that Deane's gelatine answers very well for the purpose, and the specimens which have just been mentioned are now in perfect preservation, after having been in the gelatine for some six years.
It is very curious to watch the different methods by which the Serpula protrudes and withdraws itself. When it retires into the tube, it vanishes so quickly that the eye can not follow its movements, but when it protrudes itself, it does so in a very deliberate manner, seeming to feel its way cautiously toward the light, and to be ready to dart back again with or without reason.
The organs by means of which it protrudes itself are placed close to those which withdraw it. Through the foot-warts project a number of stiff, transparent bristles, which are wonderfully like the many-barbed spears of savage nations. I have an arrow of the Tonga Islands which is almost an exact reproduction of a foot-bristle of the Serpula, saving that wood and bone are substituted for the purer material of the bristle. The shaft runs quite straight, but toward the tip the bristle is flattened and widened into a head just like that of a spear. The head has a very slight curve, is sharply pointed, and is armed with a double row of barbs on the edge. A great number of these bristles are clustered together, so that their united force is really considerable.