Tentacles are hollow; but in some cases the tentacle may become solid by obliteration of its cavity.
From the broader portion of the planula an outgrowth arises which becomes the first tentacle of the cormus.
The base of a tentacle bisected in the middle line.
It would be necessary to regard this structure as a secondary extension of the endoderm in the tentacle-web, on Allman's theory, or between the outgrowths of the hydrorhiza, on Mechnikov's hypothesis.
As a result of this extension of the umbrellar margin, all structures belonging to this region, namely, the ring-canal, the nerve-rings, and the rim of thickened ectoderm, do not run an even course, but are thrown into festoons, caught up under the insertion of each tentacle in such a way that the ring-canal and its accompaniments form in each notch of the umbrellar margin an inverted V, the apex of which corresponds to the insertion of the tentacle; in some cases the limbs of the V may run for some distance parallel to one another, and may be fused into one, giving a figure better compared to an inverted Y.
The rhodalome of some Rhodalidae, consisting of siphon, tentacle and one or more gonophores.
The athorome of Physophora, &c., consisting of siphon, tentacle, one or more palpons with palpacles, and one or more gonophores.
Similarly the ring-canal runs round the edge of the lobe as the so-called festoon-canal, and then runs upwards under the peronium to the base of the tentacle as one of a pair of peronial canals, the limbs of the V-like figure already mentioned.
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.
Naturally, it is among the free living forms that the parapodium is best developed, and least developed among the tubicolous belongs typically a long tentacle, the cirrus, which 'r podium or neuropodium, and may be developed into an arborescent gill or into a flat scale-like process, A the elytron (in Polynoe, &c.).
They are found one on each cephalic tentacle, and are simply minute open pits or depressions of the epidermis, the epidermic cells lining them being pigmented and connected with nerves (compare fig.
Supposing the tube to be completely introverted and to commence its eversion, we then find that eversion may take place, either by a forward movement of the side of the tube near its attached base, as in the proboscis of the Nemertine worms, the pharynx of Chaetopods and the eye-tentacle of Gastropods, or by a forward movement of the inverted apex of the tube, as in the proboscis of the Rhabdocoel Planarians, and in that of Gastropods here under consideration.
So too the acrembolic eye-tentacle of the snail has a complete range of movement, and also the pleurembolic proboscis of the Rhabdocoel prostoma.
Foot with anterior transverse groove; a posterior pallial tentacle; generally burrowing.
Posterior cephalic tentacle; and b, the eyes.
D, 1, e, Three pairs of tentacle-like processes placed at the sides of the mouth, and developed (in all probability) from the fore-foot.
Shell with medium spire, external or partly covered by the mantle; genital aperture below the right posterior tentacle; genital apparatus generally provided with a dart-sac and multifid vesicles.
22 and 28); it gives off a branch to each tentacle, and these all anastomose at the base of the tentacles with the second nerve of the arm, the so-called secondary arm-nerve.
Tentacles retractile into an introvert ("tentacle-sheath").
Jullien believed that this pore opens into the tentacle-sheath, but it appears probable that it really communicates with the compensation-sac and not with the tentaclesheath.
From the ring-canal are given off tentacle-canals which run down the axis of each tentacle; in many cases, however, the cavity of the tentacle is obliterated and instead of a canal the tentacle contains a solid core of endoderm.
Oesophagus, stomach, radial canals, ring-canal and tentacle-canals, constitute together the gastrovascular system and are lined throughout by endoderm, which forms also a flat sheet of cells connecting the radial canals and ring canal together like a web; this is the so-called endoderm-lamella (e.l.), a most important feature of medusan morphology, the nature of which will be apparent when the development is described.
Their appearance and position suggest that they are in some way related morphologically to the gill-plates, the anterior labial tentacle being a continuation of the outer gill-plate, and the posterior a continuation of the inner gill-plate.
I, Each such body has a basal hollow portion (en) sur mounted by a glandular cushion (kl), from the centre of which projects a small, solid; club-shaped process or tentacle (t').
Each tentacle is to the stem of a plant, and is repre sented with the base of attachment a glove-finger like outpush uppermost; the mouth, not actually ing of the whole wall of the seen in the drawing, is at the lower sac and contains typically extremity of the body, surrounded a prolongation of its internal by the circle of tentacles.
2.-I, Portion of epithelium from the tentacle of an Actinian, showing three supporting cells and one sense cell (sc); 2, a cnidoblast with enclosed nematocyst from the same specimen; 3 and 4, two forms of gland cell from the stomodaeum; 5a, 5b, epithelio-muscular cells from the tentacle in different states of contraction; 5c, an epithelio-muscular cell from the endoderm, containing a symbiotic zooxanthella; 6, a ganglion cell from the ectoderm of the peristome.
There is indeed a perfectly definite transverse septum which divides the body-cavity in the region of the tentacle-bases.
The uppermost is a purely muscular cell from the sub-umbrella; the two lower are epidermo-muscular cells from the base of a tentacle; the upstanding nucleated portion forms part of the epidermal mosaic on the free surface of the body.
On the floor of the stomach are borne the conspicuous gonads (ov), and also tentacle-like processes termed gastric filaments or phacellae, projecting into the cavity of the stomach.
Clark.) Rudimentary tentacle of the tentaculocyst.
1, with the addition of T, prostomial tentacle; Pa, parapodium.
- Free medusae with rhopalia of the normal type; the exumbrella is divided by a circular, so-called coronal groove, into two parts, a central portion, which is conical, thimble-shaped, or domed in form, and a peripheral portion, the pedal zone, which bears the marginal lobes, tentacles and rhopalia; the pedal zone is subdivided into areas termed pedalia, from each of which arises a tentacle or rhopaliurn in the interspace between two adjacent lobes of the margin.
Considering the imprisonment of the ostracod body within the valves, it is more surprising that the Asteropidae and Cypridinidae should have a pair of compound and sometimes large eyes, in addition to the e median organ at the base of I the " frontal tentacle," than 6 that other members of the group should be limited to P that median organ of sight, or have no eyes at all.
In many cases it appears that only the brilliantly coloured tentacle is pecked off by the bird, and as the snail can easily regenerate a new one, this in turn becomes infected by a fresh branch of the sporocyst ramifying through the snail and thus a new supply of larvae is speedily provided (Heckert).
Each cansists of an eversible hollow tentacle provided with hooklets and capable of introversion within a mem The excretory organs consist of flame-cells, richly convoluted canaliculi, and a pair of longitudinal canals leading to the exterior by one or more pores.
A, mouth; b, cephalic tentacle; h, gill (ctenidium).
B, The same, partially everted by eversion of the sides, as in the Nemertine proboscis and Gastropod eye-tentacle = pleurecbolic.
Shell with prominent spire; distant from right tentacle, generally appendiculated; brackish water or fluviatile.
Tw, Tentacle root.
E, Siphon with branched grappling tentacle, f.
Modifications of a tentacle, as in Trachylinae, or developed from the margin of the umbrella, in no connexion with a tentacle (or, if so connected, not producing any modification in the tentacle), as in Leptolinae.