Sessile, stalked, with eight shallow marginal lobes bearing one or more rows of tentacles; without tentaculocysts; with four gonads.
If fertile they become free medusae or sessile gonophores.
Some trees of the sessile-fruited oak bear sweet acorns in Britain, and several varieties were valued by the ancient Italians for their edible fruit.
Pedunculata, has the acorns, generally two or more together, on long stalks, and the leaves nearly sessile; while in the other, Q.
The large sessile acorns are longer than those of Q.
From the bionomical point of view, the medusa is to be considered as a means of spreading the species, supplementing the deficiencies of the :" Ca sessile polyp. It may be, however, that increased reproductiveness becomes of greater importance to the species than wide diffu sion; such a condition FIG.
The polyp is regarded, on this view, as a form phylogenetically older than the medusa, in short, as nothing more than a sessile actinula.
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.).
If a polyp, such as Hydra, be regarded simply as a sessile actinula, we must certainly consider the polyp to be the older type, and it may be pointed out that in the Anthozoa only polyp-individuals occur.
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.
When sessile gonophores are produced, they may show all stages of degeneration.
Trophosome polyps forming branching colonies of which the stem and main branches are thick and composed of a network of anastomosing coenosarcal tubes covered by a common ectoderm and supported by a thick chitinous perisarc; hydranths similar to those of Coryne; gonosome, sessile gonophores.
An important variation is seen, in the form of the hydrotheca itself, which may come off from the main stem by a stalk, as in Obelia, or may be sessile, without a stalk, as in Sertularia.
Trophosome as in Eucopidae; gonosome, sessile gonophores.
- Hydrothecae sessile, biserial, alternating or opposite on the stem.
- Hydrothecae sessile, biserial on the main stem, uniserial on the lateral branches or pinnules, which give the colony its characteristic feathery form; with nematophores.
- Metagenetic colony-forming Hydromedusae, in which the polyp-colony forms a massive, calcareous corallum into which the polyps can be retracted; polyp-individuals always of two kinds, gastrozoids and dactylozoids; gonosome either free medusae or sessile gonophores.
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.
The most usual condition, however, is that in which sessile medusoid gonophores or sporosacs are produced.
The independent plant which is generally attached to the soil by hair-like structures is the sexual generation, the sporophyte is a stalked or sessile capsule which remains always attached to the gametophyte from which it derives the whole or part of its nourishment.
It was succeeded by the sessile-fruited oak, which was in turn supplanted by the pedunculate form of the same tree.
In diameter, sessile, and generally in pairs, and are made up of large angular scales, slightly convex exteriorly, and with a sharp point in the centre.
In many Gastropoda the eyes are not thus sessile but raised upon special eye-tentacles (figs.
It is most commonly found in sessile FIG.
It carries two pairs of cephalic tentacles and a pair of sessile eyes.
The term "water-snails" includes the whole of the remaining sub-order of the Pulmonata, namely, the Basommatophora, in which the eyes are sessile, with the exception of the Auriculidae.
The group may be defined as follows: Sessile solitary Coelomata with bivalved shells usually of unequal size and arranged dorso-ventrally.
The ovary bears a sessile stigma and is more or less completely two-celled, with two erect ovules in each cell.
Perforatum, small shrubby plants with slender stems, sessile opposite leaves which are often dotted with pellucid glands, and showy yellow flowers.
This sub-order, characterized by the " sessile," broad-based abdomen, whose fist segment is imperfectly united with the thorax, and by the usually caterpillar-like larvae with legs, includes the various groups of saw-flies.
The cup-shaped flowers have six regular segments in two rows, as many free stamens, and a three-celled ovary with a sessile stigma, which ripens into a leathery many-seeded capsule.
- In this division the body is partly covered by a broad shield, united in front with the head; the eyes are sessile, the first antennae are small, the second rudimentary or wanting; of the numerous feet, sometimes sixty-three pairs, exceeding the number of segments to which they are attached, the first pair are more or less unlike the rest, and in the female the eleventh have the epipod and exopod (flabellum and sub-apical lobe of Lankester) modified to form an ovisac. Development begins with a nauplius stage.
The yellow stamen-bearing flowers are in sessile, nearly spherical catkins; the fertile ones vary in colour, from red or purple to greenish-white, in different varieties; the erect cones, which remain long on the branches, are above an inch in length and oblong-ovate in shape, with reddish-brown scales somewhat waved on the edges, the lower bracts usually rather longer than the scales.
Many parasitic hyphae put out minute lateral branches, which pierce the cell-wall of the host and form a peg-like (Trichosphaeria), sessile (Cystopus), or stalked (Hemileia), knot-like, or_a B FIG.
When a leaf has a distinct stalk it is petiolate; when it has none, it is sessile, and if in this case it embraces the stem it is said to be amplexicaul.
By longitudinal segmentation we have a leaf formed consisting of sheath, stalk and blade; or one or other of these may be absent, and thus stalked, sessile, sheathing, &c., leaves are produced.
24) the true leaves are stalked and crenate, while the stipules s are large, sessile and pin natifid.
The flowers are solitary in the leaf-axils as in pimpernel, money-wort, &c., or umbelled as in primrose, where the umbel is sessile, and cowslip, where it is stalked, or in racemes or spikes as in species of Lysimachia.
The female flowers are small, sub-globose and sessile, i It has been supposed that the origin is to be found in O.
There are at least seven orders: the stalk-eyed Brachyura, Macrura, Schizopoda, Stomatopoda, and the sessile-eyed Sympoda, Isopoda, Amphipoda.
Sympoda (or Cumaceans), in spite of their sessile eyes, have closer affinities with the stalk-eyed orders.
- This order of sessile-eyed decapods was absolutely unknown to science till 1779.
Eminent naturalists were still debating whether in this group there were eyes or no eyes, whether the eyes were stalked or sessile, whether the animals observed were larval or adult.
- As in the genuine Isopoda, the eyes of Amphipoda are always sessile, and generally paired, and, in contrast to crabs and lobsters, these two groups have only four pairs of mouthorgans instead of six, but seven pairs of trunk-legs instead of five.
As cultivated it is an annual with an erect stalk rising to a height of from 20 to 40 in., with alternate, sessile, narrowly lance-shaped leaves, branching only at the top, each branch or branchlet ending in a bright blue flower.
The leaves are rather short, curved, and often twisted; the male catkins, in dense cylindrical whorls, fill the air of the forest with their sulphur-like pollen in May or June, and fecundate the purple female flowers, which, at first sessile and erect, then become recurved on a lengthening stalk; the ovate cones, about the length of the leaves, do not reach maturity until the autumn of the following year, and the seeds are seldom scattered until the third spring; the cone-scales terminate in a pyramidal FIG.
They are chiefly pelagic organisms, floating at or near the surface of the water, but occur also at great depths, and are sometimes fixed and sessile in habit.
As already stated, a medusa of this order may be free-swimming or sessile in habit.
A well-known example of a permanently sessile form is Lucernaria, common on the Atlantic coasts of Europe, especially in Zostera-beds, attached to the weed.
- Medusae of deep pyramidal form, often sessile, attached by a stalk developed from the centre of the exumbral surface; rhopalia absent or represented by colletocystophores.
- Sessile, stalked, with capitate tentacles arranged in groups on eight projecting marginal lobes.
Sessile, with the margin undivided; with eight colletocystophores and eight adradial groups of capitate tentacles.
In the development of the Phyllopod Branchipus, the eyes are at first sessile, and the lateral lobes of the head on which they are set grow out and become movably articulated, forming the peduncles.
The entocodon, however developed, gives rise at first to a closed cavity, representing a closing over of the umbrella, temporary in the bud destined to be a free medusa, but usually permanent in the sessile gonophore.
A conical, thorn-like projection from the base of the pore, sometimes found also in dactylopores; sessile gonophores.
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.