On the upper side of the posterior end of the foot is placed the horny, concentric operculum or door.
When the animal withdraws into its shell the head first disappears with its appendages and the siphon, and the foot is doubled up in the middle, the operculum shutting in last and closing the interior against all enemies.
Mouth circular (whence its name) and provided with a thick shelly operculum which closes the orifice when the animal retires by means of an elastic ligament.
Operculum made of plates rising one above another formed at different stages of growth.
The clausilium (little door) is an internal contrivance fastened to the pillar of the shell (whereas an operculum is attached to the body of a mollusc) by an elastic ligament to protect it against insect enemies when the animal withdraws.
The eyes in this genus are not on foot-stalks; the operculumis shelly instead of horny).
Operculum semi-lunar, orange, with a projection which serves as a lock to keep the operculumin position.
The operculum expands medially to merge with the main part of the otic capsule (Fig.
The lateral edge of the operculum expands ventrally and then dorsomedially to form a complete tube.
Posteriorly the operculum increases in size, and the pars interna plectri and pars media plectri are reduced (Fig.
The lateral part of the otic capsule posterior to the terminus of the operculum and the ventromedial and dorsomedial parts of the neurocranium remain unossified.
In a group of specimens, I could not touch one even most delicately with a needle, without all the adjoining ones instantly withdrawing their cirri; it made no difference if the one touched had its operculum already closed and motionless.
I may here remark that, in most sessile Cirripedes, the outside membrane connecting the operculum and shell, is regularly moulted.
The radiate operculum of the central capsule, with the proboscis.
The double contoured outer membrane exhibits only one opening, with a radiate operculum and long proboscis.
Between the mouth of the two rhinocannae is prominent the proboscis of the astropyle, arising from the radiate operculum of the central capsule.
The opening left by this operculum is semi-lunar, and at the bottom of the cavity is a white pellicle of considerable tension, and shining like a little mirror.
The principal opercular bone or operculum of fishes.
An ingredient of the Mosaic incense, probably the operculum of some kind of strombus.
Neither of the fissures of Sylvius is quite closed, the left less so than the right; the operculum is but slightly developed, and the island of Reil lies with its fissures almost entirely uncovered.
That of medium strength raises the little bubbles on the tubes and is found to colour the ampulla and the operculum a strong red; the weaker one is found to colour them a light red, and the stronger one to break the tubes.
Muffle Tegula Muffel Latin, literally "Roof-tile" Operculum Operculum Helm oder Helmet or cover alembick for a distillation jar Orpiment Auripigmentum Operment Yellow sulphide p.
When the powerful vapour appears, the aqua gives off a kind of oil, and the operculum becomes red.
In a similar way the spout of the operculum is joined by linen covered with lute to another glass ampulla which receives the distilled aqua.
Another way is to place broken ore in a gourd-shaped earthen vessel, put it in the assay furnace, and cover with an operculum which has a long spout; under the spout, put an ampulla to receive the quicksilver which distills.
But, lest the vapours should escape from the ampulla and the operculum in that part where their mouths communicate, they are entirely sealed all round.
The operculum is likewise made of glass, and is closely joined to the ampulla with linen, cemented with wheat flour and white of egg moistened with water, and then lute free from salt is spread over that part of it.
Conch of ear very large, elliptical, extending from the base of the lower jaw to near the top of the head, with an anterior semicircular operculum in its whole length.
Feathers margining the operculum with the shaft and webs undeveloped.
Conch of the ear semicircular, extending from over the anterior angle of the eye to the middle of the lower jaw; aperture large, somewhat square, with an anterior operculum fringed with feathers.
This history was told me, and the nest with its operculumshewn me by the late Dr.
The rim of the capsule, from which the operculum has separated, forms its mouth, and this often exhibits a fringe of teeth (figs.
The calyptra is dimidiate; the operculum is present (fig.
A few inches beneath the water this operculum or lid is not unlike a pearl, but as you gaze upon it, it slips on one side, and five animated red rays appear, waving like automatic flag signals.
In the specimen to which I refer the pigmentation instead of being present on both sides was reversed: the lower side was pigmented from the posterior end to the edge of the operculum (Plate II, fig.
Sole which was entirely white on the lower side, and also on the upper, which was pigmented only over the head region from the free edge of the operculum forwards.
The operculum becomes stained intensely red by carmine, yellow by nitric acid, corresponding to the ectocapsa, the main-opening of which is closed by it.
The dark phaeodium is of about the same volume as the central capsule, and envelops its oral half with the radiate operculum and the proboscis of the astropyle.
The latter exhibits a large circular opening with thickened margin, when the radiate operculum is taken from it.
The radiate operculum of the astropyle opens by a tubular prolongation or proboscis, which is very long in the former, shorter in the latter.
But I am convinced now, by numerous experiments and observations, that the radiate operculum is a part of the outer, not of the inner membrane.
Perhaps the small cups of Catinulus may be derived from the simple rings of Mesocena, by development of an operculum on one side of the ring.
The spine surmounting the operculum exhibits a double cannelure connected with a conical cavity excavated in the thickness of the base of the opercular bone.
The most curious genus among the fishes belonging to this family is Holacanthus, in which the præoperculum is provided with an enormous spine like that of the Weever.
Operculum and opercular spine of the Lesser Weever 298 Fig.
Daldorf called it Perca scandens, and affirmed that he himself had taken one of these fishes, clinging by the spine of its operculum in a slit in the bark of a palm (Borassus flabelliformis) which grew near a pond.
The male again moved into position at the lower left edge of the operculum of the female as at Station 29-G.
The worm has a wreath of plumelike and often bright-colored gills around its head, and usually an operculum to close the aperture of its tube when it retracts.
One of the dorsal plates of the operculum of a cirriped.
One of the two lower valves of the operculum of a barnacle.
Defn: Having few spirals, or whorls; as, a paucispiral operculum or shell.
Defn: The principal opercular bone or operculum of fishes.
Spiral operculum, an operculum whih has spiral lines of growth.
The calyx is triangular in section, pointed below, and the operculum is attached to it by hinge-like teeth.
In this Devonian genus there is a single semicircular operculum furnished with a stout median septum and numerous feebly developed secondary septa.
These molluscs occur at heights varying from one or two feet to eight or nine feet above the high-water level; and they possess an unusually delicate operculum as compared with those of other species of the same family.
The Coenobita, with its stout pincers, prefers shells much smaller, relatively speaking, and ensconces itself snugly in the body whorl, forming an operculum with its claws.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "operculum" in a variety of sentences. We hope that you will now be able to make sentences using this word. Other words: cap; cover; lid; stopper; top
