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.
When standing in dense woods the trees are rather straight and formal in early growth, especially the sessile-fruited kinds, and the gnarled character traditionally assigned to the oak applies chiefly to its advanced age.
The large sessile acorns are longer than those of Q.
- Clavatella prolifera, ambulatory are known of sessile medusa.
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 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.
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.
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.
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.
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.
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.
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.