Medusa (biology)

“ In this the medusa comes nearer to man than the radiolarian. Some of the cells see to the reproduction of the medusa. Ova and spermatozoa are detached from the cell-community of the medusa’s body, blend together, and thus form the germ of a new medusa. In most cases the process is curious enough. From the germ-cell we get at first, not a real medusa, but a polyp that attaches itself to the ground, a little creature that may be remotely compared to the pretty water-lilies that meet the eye in an aquarium. Then the polyp produces something like a plant that grows buds, the real medusæ ”

“ The bodies thus detached have all the characteristics of the fully-developed medusæ. Each consists of an umbrella-shaped disk divided along its margin into lobes, generally eight in number, and of a stomach terminating in a probosciform mouth. As the creature grows, the spaces between the marginal lobes fill up; from its border long tentacles are developed, and a fringe of tendril-like filaments sprout forth from the margin. The young medusa eats voraciously, and grows proportionately large ”

“ I have never known a naked-eyed Medusa survive an exposure of fifteen minutes; but they may survive 250 an exposure of ten, and generally survive an exposure of five. But although they thus continue to live for an indefinite time, their vigour is conspicuously and permanently impaired; while in the fresh water irritability persists for a short time after spontaneity has ceased, and the tentacles and manubrium are strongly retracted. ”

“ The medusa always reproduces itself sexually, and in some cases non-sexually also. The non-sexual reproduction takes the form of fission, budding or sporogony, the details of which are described below. Buds may be produced from the manubrium, radial canals, ring-canal, or tentacle-bases, or from an aboral stolon (Narcomedusae) . In all cases only medusa-buds are produced, never polyp-buds.
The mesogloea of the medusa is largely developed and of great thickness in the umbrella. The sub-epithelial tissues, i.e. ”

“ But the medusa after three or four cycles becomes the medusa again, not, we say, by these same processes of nutrition and waste, but by a series of generations, each one involving an actual birth and an actual death. Why this difference? Surely only because the changes in the offspring of the medusa are marked by the leaving a little more husk behind them, and that husk less shrivelled, than is left on the occasion of each change between the caterpillar and the butterfly. A little more residuum, which residuum, it may be, can move about ”

“ The reader is doubtlessly aware that the title of Medusa is given to these creatures on account of the trailing fibres that surround the disc, just as the snaky locks of the mythological heroine surrounded her dreadful visage. Many species deserve the name by reason of the exceeding venom of their tresses, which are every whit as terrible to a human being as if they were the veritable vipers of the ancient allegory. ”

“ Words cannot express the exceeding beauty and grace of the Medusa, as it slowly pulsates its way through the water, rotating, revolving, rising, and sinking with slow and easy undulations, and its surface radiant with rich and changeful hues, like fragments of submarine rainbows. ”

“ The theory that the medusa is an independent individual, fully equivalent to the polyp in this respect, is now universally accepted as being supported by all the facts of comparative morphology and development. ”

“ The story of Medusa thou hast known.
FAUST Ay, verily! a corpse's eyes are those,
Which there was no fond loving hand to close.
That is the bosom I so fondly press'd,
That my sweet Gretchen's form, so oft caress'd!
MEPHISTOPHELES Deluded fool! 'Tis magic, I declare!
To each she doth his lov'd one's image wear.
FAUST What bliss! what torture! ”

“ In primitive forms the medusa-individuals are set free before reaching sexual maturity and do not contribute anything to the colony. In other cases, however, the medusa-individuals become sexually mature while still attached to the parent polyp, and are then not set free at all, but become appanages of the hydroid colony and undergo degenerative changes leading to reduction and even to complete obliteration of their original medusan structure. ”

“ In many genera and species the medusome is set free as a minute jelly-fish or Medusa, which grows and develops as an independent organism until the time when the sexual cells are ripe, and then apparently it dies. In other Gymnoblastea the medusome either in the female or the male or in both sexes does not become detached from the parent hydrosome, but bears the ripe sexual cells, discharges them into the water, and degenerates without leading an independent life at all. ”

“ Its movements in swimming are said to resemble exactly the alternating strokes given by the medusa to the liquid element, and have the same effect, causing the animal to raise itself from the bottom, and to advance back foremost even more rapidly than the medusa. It has ten very slender rays with numbers of long beards on the sides. The body, which is of a deep rose colour, is small and surrounded with ten little filiform rays. The extremities of these organs are shaped like claws, by means of which the animal [275] attaches itself to various kinds of sea-weed, and other submarine objects. ”

“ The hydrosome produces at a certain season of the year a number of buds, which develop into small bell-like jelly-fish called the "Medusae," which swim away from the parent stock and produce the sexual cells. The Medusa (Fig. 126) consists of a delicate dome-shaped contractile bell, perforated by radial canals and fringed with tentacles; and from its centre there depends, like the clapper of a bell, a tubular process, the manubrium, which bears the mouth at its extremity. This free-swimming sexual stage in the life-history of Obelia is called the "medusome." ”

“ In any case, they seem to have the power of localization. Mr. Romanes says, [GS] "A medusa being an umbrella-shaped animal, in which the whole of the surface of the handle and the whole of the concave surface of the umbrella is sensitive to all kinds of stimulation, if any point in the last-named surface is gently touched with a camel-hair brush or other soft (or hard) object, the handle or manubrium is (in the case of many species) immediately moved over to that point, in order to examine or brush away the foreign body." ”

“ If the three principal organ-systems of the medusa, namely mouth, tentacles and umbrella, be considered in the light of phylogeny, it is evident that the manubrium bearing the mouth must be the oldest, as representing a common property of all the Coelentera, even of the gastrula embryo of all Enterozoa. ”

“ The whole theory is one most intimately connected with the question of the relation between polyp and medusa, to be discussed presently. It will be seen elsewhere, however, that whatever view may be held as to the origin of metagenesis in Hydromedusae, in the case of Scyphomedusae (q.v.) no other view is possible than that the alternation of generations is the direct result of larval proliferation. ”

“ To produce a medusa the actinula grows greatly along a plane at right angles to the vertical axis of the body, whereby the aboral surface of the actinula becomes the ex umbrella, and the peristome becomes the sub umbrella. The crown of tentacles thus comes to form a fringe to the margin of the body, and the hypos tome becomes the manubrium. As a result of this change of form the gastric cavity or coelenteron becomes of compressed lenticular form, and the endoderm lining it can be distinguished as an upper or exumbral layer and a lower or subumbral layer. ”

“ Small molluscs, young crustaceans, and worms, form their ordinary food. In spite of their shape, they are most voracious, and snap up their prey all at one mouthful, without dividing it. If their prey resists and disputes with it, the Medusa which has seized it holds fast, and remains motionless, and, without a single movement, waits till fatigue has exhausted and killed its victim, when it can swallow it in all security.
In respect to size, the Medusæ vary immensely. Some are very small, while others attain more than a yard in diameter. Many species are phosphorescent during the night. ”

“ Thamnostylus, Cytaeis, &c., are other medusae with unknown hydroids. Hydractinia (figs. 9, 10) is a familiar hydroid genus, bearing gonophores.
3. Cladonemidae.—Trophosome, polyps with two whorls of tentacles, the lower filiform, the upper capitate; gonosome, free medusae, with tentacles solid and branched. The type-genus Cladonema (fig. 20) is a common British form.
4. Clavatellidae.—Trophosome, polyps with a single whorl of capitate tentacles; gonosome, free medusae, with tentacles branched, solid. Clavatella (fig. 21) , with a peculiar ambulatory medusa is a British form. ”

“ See the treatise of Delage and Hérouard (Hydrozoa, [4] ) , and the article Graptolites.
Order V. Trachylinea.—Hydromedusae without alternation of generations, i.e. without a hydroid phase; the medusa develops directly from the actinula larva, which may, however, multiply by budding. Medusae with sense-organs represented by otocysts derived from modified tentacles (tentaculocysts) , containing otoliths of endodermal origin, and innervated from the ex-umbral nerve-ring. ”

“ If we place a very irritable medusa on a pewter plate, and strike against the plate with any sort of metal, the slight vibrations of the plate are sufficient to make this animal emit light. Sometimes, in galvanising the medusa, the phosphorescence appears at the moment that the chain closes, though the exciters are not in immediate contact with the organs of the animal. ”

“ Dendroclavidae.—Trophosome, polyp with filiform tentacles in three or four whorls. Dendroclava, a hydroid, produces the medusa known as Turritopsis.
9. Clavidae (including the medusa-family Tiaridae (figs. 27 and 51) . Trophosome, polyps with scattered filiform tentacles; gonosome, medusae or gonophores, the medusae with hollow tentacles. Clava (fig. 5) , a common British hydroid, produces gonophores; so also does Cordylophora, a form inhabiting fresh or brackish water. Turris produces free medusae. Amphinema is a medusan genus of unknown hydroid. ”

“ Some of the smaller species of the Medusa (sea-nettle) are exquisitely beautiful: their form is nearly oval, varied with serrated longitudinal lines; they are extremely tender, and by no means which I am acquainted with can be preserved, for they soon dissolve in either spirit of wine or water, and lose every vestige of their shape, and indeed of their substance: the larger species are found in mis-shapen masses of many pounds weight ”

“ They vary immensely in size, ranging from minute jelly-bags, without limbs or heads, mouths or stomachs, to great masses of jelly-like substance, with eyes and mouths and powerful stinging apparatus.
All these are included in the circle of near relatives to the “Medusæ,” which name was first bestowed upon the anemones from a supposed likeness between the snaky tresses of the mythological Medusa and the tentacles of these soft-bodied animals.
“Ocean-flowers,” many of them may truly be called, since they live and grow, rooted like a plant to one spot ”

“ A remarkable echo was heard in the evening: whilst the cook was chopping his wood every blow was echoed round the bight, although we were eight miles from the shore. After leaving Port Keats we met with large quantities of a very beautiful species of medusa, it appeared to be the Medusa panopyra, figured in Peron's Atlas, (Plate 31 figure 2) . It is from this animal that the French have named their Banc des Meduses. No turtle or snakes had for some time been seen and very few sharks; but other fish were numerous. ”

“ The jelly-fish of the Mediterranean is repulsive. Contact with that animated gelatinous substance which envelopes the bather, in which the hands sink, and the nails scratch ineffectively; which can be torn without killing it, and which can be plucked off without entirely removing it—that fluid and yet tenacious creature which slips through the fingers, is disgusting; but no horror can equal the sudden apparition of the devil-fish, that Medusa with its eight serpents.
No grasp is like the sudden strain of the cephaloptera.
It is with the sucking apparatus that it attacks. ”

“ In the same tanks a small hydroid, very similar to Microhydra, has been found, which bears medusa-buds and is probably the stock from which the medusa is budded. It is a remarkable fact that all specimens of Limnocodium hitherto seen have been males; it may be inferred from this either that only one polyp-stock has been introduced into Europe, from which all the medusae seen hitherto have been budded, or perhaps that the female medusa is a sessile gonophore, as in Pennaria. ”

“ When the roving medusa has sown its wild-oats, and comes to settle down into a respectable family hydroid, it loses all these advantages belonging to its wandering life, and becomes in its later form identical with the parent ”

“ But although the locomotor centres of a covered-eyed Medusa are thus, generally speaking, more diffused than are those of a naked-eyed Medusa, if we consider the organism as a whole, the locomotor centres in the margin of a covered-eyed Medusa are less diffused than are those in the margin of a naked-eyed Medusa. In no case does the excision of the margin of a swimming organ produce any effect upon the movements of the manubrium. ”

“ But, what is stranger still, Mr M'Cready has recently discovered in the harbour of Charleston in North America, a Medusa which is parasitic upon another Medusa. Cunina octonaria does not swim freely in the water, but inhabits the cavity of the bell of Turritopsis nutricula. "Not only does the latter furnish a shelter and dwelling-place for the larvæ during their development; it also serves as their nurse, by allowing the parasites, whilst adhering by their tentacles, to draw [Pg 375] nourishment out of its mouth by means of a large proboscis. ”