Medusa Sentence Examples
The endoderm of the medusa shows the same general types of structure as in the polyp, described above.
It is evident that the outer envelope of the gonophore represents the ex-umbral ectoderm (ex.), and that the inner ectoderm lining the cavity represents the sub-umbral ectoderm of the free medusa.
Finally, a mouth is formed by breaking through at the apex of the manubrium, and the now fully-formed medusa becomes separated by rupture of the stalk of the bud and swims away.
It is seen from the foregoing account of medusa - budding that the entocodon is a very important constituent of the bud, furnishing some of the most essential portions of the medusa; its cavity becomes the subumbral cavity, and its lining furnishes the ectodermal epithelium of the manubrium and of the sub-umbral cavity as far as the edge of the velum.
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.Advertisement
The special property of the medusa is the umbrella, distinguishing the medusa at once from other morphological types among the Coelentera.
In Trachylinae the development produces always a medusa, and there is no polyp-stage.
The polyp is regarded, on this view, as a form phylogenetically older than the medusa, in short, as nothing more than a sessile actinula.
The whole theory is one most intimately connected with the question of the relation between polyp and medusa, to be discussed presently.
For the most part, polyp and medusa have been regarded as modifications of a common type, a view supported by the existence, among Scyphomedusae (q.v.), of sessile polyp-like medusae (Lucernaria, &c.).Advertisement
In some polyps the tentacles are webbed at the base, and it was supposed that a medusa was a polyp of this kind set free, the umbrella being a greatly developed web or membrane extending between the tentacles.
Mechnikov considered the plate thus formed at the base of the polyp as equivalent to the umbrella, and the body of the polyp as equivalent to the manubrium, of the medusa; on this view the marginal tentacles almost invariably present in medusae are new formations, and the tentacles of the polyp are represented in the medusa by the oral arms which may occur round the mouth, and which sometimes, e.g.
The question is one intimately connected with the view taken as to the nature and individuality of polyp, medusa and gonophore respectively.
The theory that the medusa is simply an organ, which has become detached and has acquired a certain degree of independence, like the well-known instance of the hectocotyle of the cuttle-fish.
Huxley, the sporosac is the starting-point of an evolution leading up through the various types of gonophores to the free medusa as the culminating point of a phyletic series.Advertisement
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.
Balfour put forward the view that the polyp was the more primitive type, and that the medusa is a special modification of the polyp for reproductive purposes, the result of division of labour in a polypcolony, whereby special reproductive persons become detached and acquire organs of locomotion for spreading the species.
Brooks, on the other hand, as stated above, regards the medusa as the older type and looks upon both polyp and medusa, in the Hydromedusae, as derived from a free-swimming or floating actinula, the polyp being thus merely a fixed nutritive stage, possessing secondarily acquired powers of multiplication by budding.
The Hertwigs when they discovered the endoderm-lamella showed on morphological grounds that polyp and medusa are independent types, each produced by modification in different directions of a more primitive type represented in development by the actinulastage.
This must not be taken to mean, however, that the medusa is derived from a sessile polyp; it must be regarded as a direct modification of the more ancient free actinula form, without primitively any intervening polyp-stage, such as has been introduced secondarily into the development of the Leptolinae and represents 'a revival, so to speak, of an ancestral form or larval stage, which has taken on a special role in the economy of the species.Advertisement
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 typical genus is the well-known hydroid Podocoryne, budding the medusa known as Dysmorphosa; Thamnostylus, Cytaeis, &c., are other medusae with unknown hydroids.
Dendroclava, a hydroid, produces the medusa known as Turritopsis.
Nemopsidae, for the floating polyp Nemopsis, very similar to Tubularia in character; the medusa, on the other hand, is very similar to Hippocrene (Margelidae).
Obelia forms numerous polyserial stems of the characteristic zigzag pattern growing up from a creeping basal stolon, and buds the medusa of the same name.Advertisement
Aequorea is a common medusa.
The condition of things can be imagined by supposing that in a medusa primitively of normal build, with tentacles at the margin, the umbrella has grown down past the insertion of the tentacles.
In these species the actinula is parasitic upon another medusa; for instance, Cunoctantha octonaria upon Turritopsis, C. proboscidea upon Liriope or Geryonia.
The parasitic actinula is found attached to the proboscis of the medusa; it thrusts its greatly elongated hypostome into the mouth of the medusa and nourishes itself upon the food in the digestive cavity of its host.
In such cases the original parent-actinula does not itself become a medusa, but remains arrested in development and ultimately dies off, so that a true alternation of generations is brought about.
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 re markable fact that all specimens of Limnocodium hitherto seen have been males; it may be inferred from this either that only one polypstock 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.
As yet, however, the medusa of Microhydra has only been seen in an immature condition, but it shows some well-marked differences from Limnocodium, especially in the structure of the tentacles, which furnish useful characters for distinguishing species amongst medusae.
Thus the disposition of the endoderm-cavities is roughly comparable to the gastrovascular system of a medusa.
By Haeckel they are considered homologous with the umbrella of a medusa.
The gonostyles have been compared to the blastostyles of a hydroid colony, or to the manubrium of a medusa which produces free or sessile medusa-buds.
Huxley, therefore, considered a hydroid colony, for example, as a single individual, and each separate polyp or medusa budded from it as having the value of an organ and not of an individual.
Thus a bract may be regarded, with Haeckel, as a modified umbrella of a medusa, a siphon as its manubrium, and a tentacle as representing a medusan tentacle shifted in attachment from the margin to the sub-umbrella; or a siphon may be compared with a polyp, of which the single tentacle has become shifted so as to be attached to the coenosarc and so on.
According to Pindar, she imitated on the flute the dismal wail of the two surviving Gorgons after the death of Medusa.
The story of the slaying of Medusa by Athena, in which there is no certain evidence that she played a direct part, explained by Roscher as the scattering of the storm-cloud, probably arose from the fact that she is represented as wearing the Gorgon's head as a badge.
The usual attributes of Athena were the helmet, the aegis, the round shield with the head of Medusa in the centre, the lance, an olive branch, the owl, the cock and the snake.
He died from the bite of a serpent which sprang from the blood of the Gorgon Medusa.
In July 1816 the French frigate "Medusa," which carried officers on their way to Senegal to take possession of that country for France, was wrecked off Arguin, 350 lives being lost.
In the first place, we find in this group two distinct types of person or individual, the polyp and the medusa (qq.v.), each capable of a wide range of variations; and when both polyp and medusa occur in the life-cycle of the same species, as is frequently the case, the result is an alternation of generations of a type peculiarly characteristic of the class.
The morphology of the Hydrozoa reduces itself, therefore, to a consideration of the morphology of the polyp, of the medusa and of the colony.
Putting aside the last-named, for a detailed account of which see Hydromedusae, we can best deal with the peculiarities of the polyp and medusa from a developmental point of view.
The gastrula has now become an actinula, which may be termed the distinctive larva of the Cnidaria, and doubtless represents in a transitory manner the common ancestor of the group. In no case known, however, does the actinula become the adult, sexually mature individual, but always undergoes further modifications, whereby it develops into either a polyp or a medusa.
C,C', D,D', two types of medusa organization; C and D are composite sections, showing a radius (R) on one side, an interradius (IR) on the other; C' and D' are plans; the mouth and manubrium are indicated at the centre, leading into the gastral cavity subdivided by the four areas of concrescence in each interradius (IR).
Returning now to the actinula, this form may, as already stated, develop into a medusa, a type of individual found only in the Hydrozoa, as here understood.
To become a medusa, the actinula grows scarcely at all in the direction of the principal axis, but greatly along a plane at right angles to it.
It is sufficient to state here that the medusa is usually a free-swimming animal, floating mouth downwards on the open seas, but in some cases it may be attached by its aboral pole, like a polyp, to some firm basis, either temporarily or permanently.
The Hydrozoa may be defined, therefore, as Cnidaria in which two types of individual, the polyp and the medusa, may be present, each type developed along divergent lines from the primitive actinula form.
The name medusa is suggested by the tentacles, usually long and often numerous, implanted on the edge of the umbrella and bear the stinging organs of which sea-bathers are often disagreeably aware.
Hence the animals have suggested to vivid imaginations the head of the fabled Gorgon or Medusa with her chevelure of writhing snakes.
The medusa occurs as one type of individual in the class Hydrozoa, the other type being the polyp. In a typical medusa we can distinguish the following parts.
A medusa has a layer of muscles, more or less strongly developed, running in a circular direction on the surface of the subumbrella, the contractions of which are antagonized by the elasticity of the gelatinous substance of the body.
A medusa with a remarkable habit of life is Mnestra parasites, which is parasitic on the pelagic mollusc Phyllirrhoe, attaching itself to the host by its subumbral surface; its tentacles, no longer required for obtaining food, have become rudimentary.
About the foundation of Halicarnassus various traditions were current; but they agree in the main point as to its being a Dorian colony, and the figures on its coins, such as the head of Medusa, Athena and Poseidon, or the trident, support the statement that the mother cities were Troezen and Argos.
The subjects are, between two panthers, a central group of a gigantic Medusa with her two diminutive children, Pegasus and Chrysaor, and corner groups of apparently unconnected battle scenes.
When beetles, or medusae, or cats vary, the range of possible variation is limited and determined by the beetle, medusa or cat constitution, and any possible further differentiation or specialization must be in a sense at least orthogenetic - that is to say, a continuation of the line along which the ancestors of the individual in question have been forced.
As already stated, a medusa of this order may be free-swimming or sessile in habit.
F, Ephyra developing into a medusa by the growth of the adradial regions.
K, M, Mw, Ms, P, R2, ephyra grows in size it gradually takes on the form and structure of the young medusa.
Nevertheless a comparison between Lucernaria and its close ally Haliclystus shows clearly that the absence of sense-organs in the former is the result of secondary reduction, so that a true medusa may lose its most characteristic feature.
Nausithoe, a small medusa of world-wide distribution, is the type of the subfamily Nausithoidae; the subfamily Linergidae includes the genera Linerges, &c., medusae confined to tropical seas.
With equal research and no less effect he painted on another occasion the head of a snaky-haired Medusa.
In the subdivision Anthozoa, comprising the sea-anemones and corals, the individual is always a polyp; in the Hydrozoa, however, the individual may be either a polyp or a medusa.
At the wreck of the " Medusa " frigate in 1876, fifteen people survived on a raft for thirteen days without food.
Hesiod increases the number of Gorgons to threeStheno (the mighty), Euryale (the far-springer) and Medusa (the queen), and makes them the daughters of the sea-god Phorcys and of Keto.
Medusa was the only one of the three who was mortal; hence Perseus was able to kill her by cutting off her head.
The Rondanini Medusa at Munich is a famous specimen of this conception.
More recent is the explanation of anthropologists that Medusa, whose virtue is really in her head, is derived from the ritual mask common to primitive cults.
Furthermore, medusa cells (i.e. connective tissue eosinophils that have assumed an amoeboid or fibrillar shape) were readily identifiable in endometriosis specimens.
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.
The alternative is to fish all stages of the medusa in its growth in the open sea, a slow and laborious method in which the chance of error is very great, unless the series of stages is very complete.
Gunther  to belong to the same family (Cladonemidae) as Cladonema and Clavatella, and it is reasonable to suppose that the non-parasitic ancestor of Mnestra was, like the other two genera, an ambulatory medusa which acquired louse-like habits.
Allman, however, regarded this type of gonad as equivalent to a sporosac, and considered the medusa bearing them as a non-sexual organism, a " blastocheme " as he termed it, producing by budding medusoid gonophores.
In Leptolinae the actinula becomes the sessile polyp which has acquired the power of budding and producing individuals either of its own or of a higher rank; it represents a persistent larval stage and remains in a sexually immature condition as a neutral individual, sex being an attribute only of the final stage in the development, namely the medusa.
The polyp of the Leptolinae has reached the limit of its individual development and is incapable of becoming itself a medusa, but only produces medusa-buds; hence a true alternation of generations is produced.
If it is assumed that all these genera bore gonophores ancestrally, then medusa of similar type must have been evolved quite inde pendently in a great number of cases.
It would be particularly interesting to ascertain how the nematocysts of a polyp are related to those possessed by the medusa budded from it, and it is possible that in this manner obscure questions of relationship might be cleared up.
The mesogloea becomes enormously increased in quantity (hence the popular name "jelly-fish"), and in correlation with this the endoderm-layer lining the coelenteron becomes pressed together in the interradial areas and undergoes concrescence, forming a more or less complicated gastrovascular system (see Medusa).
Diagram of the structure of a medusa; the ectoderm is left clear, the endoderm is dotted, the mesogloea is shaded black; a-b, principal axis (see Hydrozoa); to the left of this line the section is supposed to pass through an inter-radius (I.R.); to the right through a radius (R).
The subclass Scyphomedusae contains a number of animals which in the adult condition are medusae or jellyfishes (see Medusa), exclusively marine in habitat and found in all seas.
Taking as a starting-point the wide archenteric cavity which the medusa inherits primitively from the antecedent actinula-stage (see article Medusa), we find, in such a form as Tessera, four interradial areas of concrescence between the exumbral and subumbral layers of endoderm, four so-called septal nodes or " cathammata," subdividing the stomach into four wide, radially situated pouches which communicate with each other beyond the septal nodes by wide apertures constituting what is termed by courtesy a ring-canal.
For some very serious fantasy lingerie, try the Wavy Medusa at Lingerie Specialists.
Topping off the look is Versace's signature Medusa logo.
Here, the Medusa logo is featured on the temples of the frame and are encrusted with Swarovski crystals.
The Medusa logo and stone embellishments on the side of the frame only add to the drama of the look.
The Versace Medusa logo or the Greek lettering logo is featured on most frames.
He also has access to Magic abilities, including the Gaze of Medusa, which can turn enemies to stone, or the Rage of Zeus, which shoots powerful lightning bolts.
You can even expand your abilities by reaching certain other Gods that are willing to support you in your cause, such as Zeus, who will let you hurl lightning at your enemies and Medusa who will let you turn them to stone for a time.
Use Crassus Medusa shield and activate its power to turn him into stone.
Use the Medusa weapon to turn him into stone, and use rage if you are able while he is immobile.
It is rare to find in the polyp a regular, symmetrical disposition of the tentacles as in the medusa.
A, A hydriform person giving rise to medusiform person by budding from th margin of the disk; B, free swimming medusa (Steenstrupia of Forbes) detached from the same, with manubrial genitali.
In the polyp the nervous tissue is always in the form of a scattered plexus, never concentrated to form a definite nervous system as in the medusa.
Hence it is convenient to consider the morphology of the medusa from these two aspects.
The manubrium is absent altogether in the fresh-water medusa Limnocnida, in which the diameter of the mouth exceeds half that of the umbrella; on the other hand, the manubrium may attain a great length, owing to the centre of the sub-umbrella with the stomach being drawn into it, as it were, to form a long proboscis, as in Geryonia.
The nervous system of the medusa consists of sub-epithelial ganglion-cells, which form, in the first place, a diffuse plexus of nervous tissue, as in the polyp, but developed chiefly on the subumbral surface; and which are concentrated, in the second place, to form a definite central nervous system, never found in the polyp. In Hydromedusae the central nervous system forms two concentric nerverings at the margin of the umbrella, near the base of the velum.
The possession of definite senseorgans at once distinguishes the medusa from the polyp, in which they are never found.
In this way the medusa sinks from an independent per sonality to an organ of the polyp-colony, becoming a so-called medusoid gonophore, or bearer of the reproductive organs, and losing gradually all organs necessary for an independent existence, namely those of sense, locomotion and nutrition.
The spore cell gives rise to a " sporelarva," which is set free in the coelenteron and grows into a medusa.
The medusa arises direct from the actinulastage and there is no entocodon formed, as in the budding described above.
Pennaria, with a free medusa known as Globiceps, is a common Mediterranean form.
The medusa has a pronounced radial symmetry, and the positions of the primary tentacles, usually four in number, mark out the so-called radii, alternating with which are four interradii.
From the stomach, canals arise termed the radial canals (r.c.); typically four in number, they run in a radial direction to the edge 2 For other variations of the medusa, often of importance for systematic classification, see Hydromedusae and Scyphomedusae.
The internal anatomy of the medusa is as variable as its external features.
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 exumbrella, and the peristome becomes the subumbrella.
The two apposed layers of endoderm in the cathammal area undergo complete fusion to form a single layer of epithelium, the endoderm-lamella of the adult medusa.
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.
In the majority of cases we do not know the polyp corresponding to a given medusa, or the medusa that arises from a given polyp.'
To establish the exact relationship it is necessary not only to breed but to rear the medusa, which cannot always be done in 1 In some cases hydroids have been reared in aquaria from ova of medusae, but these hydroids have not yet been found in the sea (Browne [Io a]).
As already stated, there occur in the Hydromedusae two distinct types of person, the polyp and the medusa; and either of them is capable of non-sexual reproduction by budding, a process which may lead to the formation of colonies, composed of more or fewer individuals combined and connected together.
The endodermal spadix (sp) of the sporosac represents the endoderm of the manubrium; the ectodermal lining of the sporosac (ex.) represents the ex-umbral ectoderm of the medusa; and the intervening layers, together with the sub-umbral cavity, have disappeared.
The budding of this medusa has been worked out in detail by Chun (Hydrozoa, ), to whom the reader must be referred for the interesting laws of budding regulating the sequence and order of formation of the buds.
The remarkable medusa Mnestra parasites is ecto-para- '"' rp m sitic throughout life sr..
If the bud, however, is destined to give rise not to a free medusa, but to a gonophore, the development is similar but becomes arrested at various points, according to the degree to which the gonophore is degenerate.
According to another story, her son Perseus, on his return with the head of Medusa, finding his mother persecuted by Polydectes, turned him into stone, and took Danae back with him to Argos.