Polyp (biology)

“ As a rule, the polyps are either male or female; but in stock-forming species individuals of the two sexes are often mixed. Monoxenia may be taken as the simplest type of the regularly radiate polyps; in all the different organs being repeated in regular rings round a central axis; the mouth also is circular. From this interesting account, drawn by Haeckel, of a simple polyp, it will be at once seen what kind of radiate animal it is that builds up the coral reefs. “No garden on earth can match the gardens of the sea that circle the northern part of Australia. ”

“ It is an almost universal attribute of polyps to possess the power of “reproducing themselves non-sexually by the method of budding. This mode of reproduction may be combined with sexual reproductiveness, or may be the sole method by which the polyp produces offspring, in which case the polyp is entirely without sexual organs. In many cases the buds formed do not separate from the parent but remain in continuity with it, thus forming colonies or stocks, which may reach a great size and contain a vast number of individuals. ”

“ In the Calyptoblastea, where the polyps are protected by special capsules of the perisarc, the gonothecae enclosing the blastostyles differ from the hydrothecae protecting the hydranths (fig. 54) .
In other colonies the two functions of the nutritive polyp, namely, capture and digestion of food, may be shared between different polyps (fig. 10) . One class of polyps, the dactylozoids (dz) , lose their mouth and stomach, and become elongated and tentacle-like, showing great activity of movement. ”

“ The species are multiplied by a kind of vegetation, one or two, or even more young ones, emerging gradually from the sides of the parent animal; and these young ones are frequently again prolific before they drop off; so that it is no uncommon thing to see two or three generations at once on the same Polyp. But the most astonishing fact respecting this animal is, that if a Polyp be cut in pieces, it is not destroyed, but is multiplied by dissection. ”

“ Thus the typical hydroid colony starts from a “founder” polyp, which in the vast majority of cases is fixed, but which may be floating, as in Nemopsis, Pelagohydra, &c. The founder-polyp usually produces by budding polyp-individuals, and these in their turn produce other buds. The polyps are all non-sexual individuals whose function is purely nutritive. After a time the polyps, or certain of them, produce by budding medusa-individuals, which sooner or later develop sexual elements ”

“ Then you will see that the slit was not exactly a slit after all, but the round edge where the sac was [pg 384] pushed in. Ah! you will say, you are now showing me a polyp like those on the sertularian tree. Not so fast, my friend; you have not studied what is still under the covering skin and hidden in the living animal. I have, however, prepared a slide with this membrane removed and there you can observe the different parts, and learn that each one of these alcoves contains a complete animal, and not merely one among many mouths, like the polyp on Sertularia. ”

“ The polyp cells are oval, placed just under the skin, and are the terminating points of certain long canals which traverse the whole polypidom. The polyps, which are distributed over the whole surface, can withdraw into the cavities; they are, besides, of an extremely vital sensibility: the least shock impresses itself on the tentacula, the impulse of a wave even producing contraction; in response, the animal, which is well developed, sallies out perceptibly, but immediately retires again to hide itself in the cell. ”

“ In the centre of the disc is the mouth, a simple opening, a mere hole in the top of a sac.
[86] Our polyp, or anemone, has no organs of locomotion, no organs of sight, taste or hearing, indeed no brain. It has at any rate the rudiments of a nervous and muscular system, for it is able to move its tentacles all towards that one which has captured prey and assist it in conveying the food to the mouth. ”

“ In case of many polyps all or some of the new individuals which arise by budding do not become polyps, but develop into medusæ or jellyfish, which separate from the fixed polyp and swim off through the water. ”

“ By budding is understood the formation of a new individual from a fresh growth of undifferentiated material. It is convenient to distinguish buds that give rise to polyps from those that form medusae.
(a) The Polyp.—The buds that form polyps are very simple in mode of formation. Four stages may be distinguished; the first is a simple outgrowth of both layers, ectoderm and endoderm, containing a prolongation of the coelenteric cavity; in the second stage the tentacles grow out as secondary diverticula from the side of the first outgrowth ”

“ Apart from larval or embryonic forms there are found typically two types of person, as already stated, the polyp and the medusa, each of which may vary independently of the other, since their environment and life-conditions are usually quite different. Hence both polyp and medusa present characters for classification, and a given species, genus or other taxonomic category may be defined by polyp-characters or medusa-characters or by both combined. If our knowledge of the life-histories of these organisms were perfect, their polymorphism would present no difficulties to classification ”

“ I have noticed that all the individuals which have produced eggs in my aquarium have been of this colour, which they have retained in spite of captivity; whereas individuals that produced spermatozoa often lost their colour completely before doing so, sometimes becoming of a milky white owing to the accumulation of minute drops of liquid in their endoderm cells. Even in green individuals there is never any trace in the cells of coloured bodies of a definite form.
The Indian polyp, unlike European representatives of its species, is a very delicate little animal. ”

“ They affix themselves to the under-parts of leaves, and to the stalks of such vegetables as happen to grow in{605} the same water; and feed on the various species of small worms and other aquatic animals within their reach. When any of these pass near a Polyp, the latter suddenly catches it with its arms, and dragging it to its mouth, swallows it by degrees, much in the same manner as a snake gorges its prey. ”

“ The buds may all become detached after a time and give rise to separate and independent individuals, as in the common Hydra, in which only polyp-individuals are produced and sexual elements are developed upon the polyps themselves; or, on the other hand, the polyp-individuals produced by budding may remain permanently in connexion with the parent polyp, in which case sexual elements are never developed on polyp-individuals but only on medusa-individuals, and a true colony is formed. ”

“ Upon the delicate branches we find little horny cups, each of which is the habitation of a tiny Polyp, furnished with a mouth and stomach, and with a circlet of slender arms to enable it to capture its prey. Other species are enclosed only in a soft membrane, but all rise from creeping roots. ”

“ Polyorama, pol-i-ō-ra′ma, n. an optical apparatus presenting many views.
Polyp, Polype, pol′ip, n. a name usually applied to an animal like the fresh-water hydra, having a tubular body, and a wreath of many tentacles round the mouth: something with many feet or roots: a pedunculated tumour attached to the surface of a mucous membrane—in the nose, &c.—also Pol′ypus:—pl. Polypes (pol′ips) , Polypi (pol′i-pī) .—ns. Pol′ypary, the horny or chitonous outer covering of a colony of polyps; Pol′ypide, an individual zoöid of a polyzoarium or compound polyzoan ”

“ The polyp may be solitary, but more usually produces polyps by budding and forms a polyp-colony. The polyp usually has the body distinctly divisible into hydranth, hydrocaulus and hydrorhiza, and is usually clothed in a perisarc. The medusae may be set free or may remain attached to the polyp-colony and degenerate into a gonophore. When fully developed the medusa is characterized by the sense organs being composed entirely of ectoderm, developed independently of the tentacles, and innervated from the sub-umbral nerve-ring. ”

“ The lowest in structure among the Polyps are not Corals, but the single, soft-bodied Actiniae. They have no solid parts, and are independent in their mode of existence, never forming communities, like the higher members of the class. It might at first seem strange that independence, considered a sign of superiority in the higher animals, should here be looked upon as a mark of inferiority. But independence may mean either simple isolation, or independence of action; and the life of a single Polyp is no more independent in the sense of action than that of a community of Polyps. ”

“ These medusæ or jellyfish produce sperm-cells and egg-cells. The sperm-cells fertilize the egg-cells and a new individual develops from each fertilized egg. This new individual is at first an active free-swimming larva called a planula, which does not resemble either a medusa or polyp. After a while it settles down, becomes fixed and develops into a polyp. Thus a polyp may produce a medusa or jellyfish which, however, produces not a new jellyfish, but a polyp. This is called an alternation of generations, and is not an uncommon phenomenon among the lower animals. ”

“ It appears again on this new level in the aggregation of hydroid polyps, of polyzoa, of ascidians, and especially in the beautiful floating Siphonophora, in which the polyp-like units (themselves historically aggregates of cells) have become so subordinate in relation to the whole that they can often scarcely be recognized as individuals, and the individuality of the aggregate is much more marked than that of its components. It appears in a new way in the Termites and in the social Hymenoptera—ants, bees, and wasps. ”

“ There are, indeed, plants floating freely in the sea, but this only in a few situations, and these are far too bulky to be swallowed by a Polyp, while it has no organs with which to detach from them smaller portions. A Polyp cannot gnaw, but is obliged to wait till a piece comes adapted to his swallow ”

“ When the young polyp is separated from the mother, it swims about, and executes all the movements peculiar to adult animals. The entrance into life and maturity takes place with these beings at one and the same moment. Infancy and youth are suppressed in this little world.
So long as the young polyp remains attached to the mother, she is the nurse; by a touching change, the young polyp nurses her in his turn. In short, the stomach of the mother and her young have communication; so that the prey swallowed by the parent passes partially into the stomach of her progeny. ”

“ Those who have attended to the habits of the polypus, which is found in the stagnant water of our ditches in July, affirm, that the young ones branch out from the side of the parent like the buds of trees, and after a time separate themselves from them. This is so analogous to the manner in which the buds of trees appear to be produced, that these polypi may be considered as all male animals, producing embryons, which require no mother to supply them with a nidus, or with nutriment, and oxygenation. ”

“ To become a polyp, the actinula (fig. 3, A) becomes attached to some firm object by the pole farthest from the mouth, and its growth preponderates in the direction of the principal axis, that is to say, the axis passing through the mouth (fig. 3, a-b) . As a result the body becomes columnar in form (fig. 3, B) , and without further change passes into the characteristic polyp-form (see Polyp) . ”

“ It lives at a depth of about a hundred feet, and is often brought to the Zoological Station by the fishermen in large quantities. Its borrowed mollusc shell often bears a little polyp, Podocoryne carnea (Fig. 34) , which forms colonies of often [Pg 164] several hundred individuals, arising from a common root-work of stolons which covers the shell. The polyp colony is composed of different kinds of individuals or personæ, illustrating the principle of division of labour: it includes (1) nutritive persons (np) which possess a proboscis, mouth, and tentacles on their club-shaped bodies ”

“ Fig. 56. A young Coral Polyp fixed upon a Rock. (Lacaze-Duthiers.)
The simple isolated state of the animal, whose phases of development we have indicated, does not last long. It possesses the property of producing new beings, as we have already said, by budding. But how is the polypidom formed? If we take a very young branch, we find in the centre of the thickness of the crust a nucleus or stony substance resembling an agglomeration of spicula. When they are sufficient in number and size, these nuclei form a kind of stony plate, which is imbedded in the thickness of the tissues of the animal. ”

“ The simplest form of polype is that of a fleshy bag open at one end, surmounted by a circle of contractile threads or fingers called tentacles. The plate shows, on a very minute scale, at figs. 1, 3, and 6, several of these little polypiform bodies protruding from their cells. But the Hydra or Fresh-water Polype has no cell, and is quite unconnected with any root thread, or with other individuals of the same species. It is perfectly free, and so simple in its structure, that when the sac which forms its body is turned inside out it will continue to perform the functions of life as before. ”

“ If the truncated portions of a polype be placed end to end, and gently pushed together, they will unite into a single one. The two portions are first joined together by a slender neck, which gradually fills up and disappears, the food passing from one part into the other; and thus we may form polypes, not only from different portions of the same animal, but from those of different animals. We may fix the head of one to the body of another, and the compound animal will grow, eat, and multiply, as if it had never been divided. ”