Various forms of Ctenophora.
a. Cestram Veneris. b. Eurhamphæa vexilligera. c. Beroë rufescens.
d. Callianira triploptera. e. Pleurobrachia pileus. (a is considerably reduced; b slightly so; c and e are about the natural size; the size of d is uncertain.)
The land has its flowers; they bloom in our gardens, they adorn our meadows, they perfume the skirts of the forest, they brave the winds that blow round the high mountain peaks, they conceal themselves in the clefts of rocks, or spring forth out of ruins; wherever a plant can find room there Flora appears with her lovely gifts.
But the ocean also has its large radiate anemones, whose lustrous petals, still more wonderful than those of the land, for they are endowed with animal life, form the chief ornament of the crystal tide-pools, or of the sheltered basins of our rock-bound shores.
More than twenty species of these marine flowers, many of them displaying a gorgeous wreath of richly coloured tentacles, are denizens of the British waters; but the finest and largest are found along the margin of the equatorial ocean, where they occasionally measure a foot in diameter. Their tints are as various as the arrangement of their prehensile crown; fiery red and apple-green, yellow and white as driven snow. Sometimes the tentacles form a gorgon's head of long thick worms, clothed in satin and velvet, and sometimes a thicket of delicate filaments.
Nothing seems more inoffensive than a sea-anemone expanding its disc in the tranquil waters, but woe to the wandering annelide, to the shrimp, or whelk, or nimble entomostracon, that comes within reach of its urticating tentacles, for, plunged into a fatal lethargy, it is soon hurried to the gaping mouth of its voracious enemy, ever ready to engulf it in a living tomb. The morsel thus swallowed is retained in the stomach for ten or twelve hours, when the undigested remains are regurgitated, enveloped in a glairy fluid, not unlike the white of an egg. The size of the prey is frequently in unseemly disproportion to the preyer, being often equal in bulk to itself. Thus Dr. Johnstone mentions a specimen of Actinia crassicornis, that might have been originally two inches in diameter, and that had somehow contrived to swallow a scallop-valve of the size of an ordinary saucer. The shell fixed within the stomach was so placed as to divide it completely into two halves, so that the body, stretched tensely over, had become thin and flattened like a pancake. All communication between the inferior portion of the stomach and the mouth was of course prevented; yet instead of emaciating and dying of an atrophy, the animal had availed itself of what undoubtedly had been a very untoward accident to increase its enjoyments and chances of double fare. A new mouth, furnished with two rows of numerous tentacula, was opened upon what had been the base, and led to the under stomach; the individual had indeed become a sort of Siamese twin, but with greater intimacy and extent in its unions.
From this instance we may naturally infer that the Actiniæ are no mean adepts in the art of accommodating themselves to circumstances. They may be kept without food for upwards of a year; they may be immersed in water hot enough to blister their skins, or exposed to the frost, or placed within the exhausted receiver of the air-pump, and their hardy vital principle will triumph over all these ordeals. Their reproductive powers are truly astonishing. Cut off their tentacles, and new ones sprout forth; repeat the operation, and they germinate again. Divide their bodies transversely or perpendicularly through the middle, and each half will develop itself into a more or less perfect individual.
But these apparently indestructible creatures die almost instantly when plunged into fresh water, which is for them, or for so many other marine animals, a poison no less fatal than prussic acid to man.
Though generally firmly attached by means of a glutinous secretion from their enlarged base to rocks, shells, and other extraneous bodies, the sea-anemones can leave their hold, and remove to another station, whensoever it pleases them, either by gliding along with a slow and almost inperceptible movement or by reversing the body and using the tentacula as feet; or, lastly, inflating the body with water so as to diminish its specific weight, they detach themselves, and are driven to a distance by the random motion of the waves. They are extremely sensible not only to external irritations—the slightest touch causing them to shrink into a shrivelled shapeless mass—but also of atmospherical changes. They hide their crown under a glare of light; but in a calm and unclouded sky expand and disclose every beauty, while they remain contracted and veiled in cloudy or stormy weather. The Abbé Dicquemare has even found, from several experiments, that they foretell changes of the weather as certainly as the barometer. When they remain naturally closed there is reason to fear a storm, high wind, and a troubled sea; but a fair and calm season is to be anticipated when they lie relaxed with expanded tentacula. The ova of the Actiniæ are detained for some time after their separation in the interseptal spaces, or even in the stomach, and there hatched, as it were, into their lasting form. On emerging into the open ocean, they already resemble their full-grown relatives, the only difference consisting in a smaller number of tentacles and septa. The sea-anemones were consequently supposed to be viviparous, an error which more accurate observations have fully refuted.
Alcyonidium elegans.
a. Branch to which the polypary is fixed. b. Foot. c. Trunk.
d. Polyp-bearing branches. e. Polyps contracted within the foot.