| 释义 |
operculum|əʊˈpɜːkjʊləm|
Pl. -la.
[a. L. operculum cover, covering, lid, f. operīre to cover, close: see -culum.]
An organ or structure forming or resembling a lid or cover; spec.
1. Zool.
a. The gill-cover of a fish; esp. the hindmost and uppermost bone of this.
1752Sir J. Hill Hist. Anim. 225 They are in great part covered by the opercula of the gills. 1849Thoreau Week Concord Sat. 31 There is also another species of bream..without the red spot on the operculum. 1880Günther Fishes 38 The operculum, forming the posterior margin of the gill-opening.
b. The calcareous, horny, or fibrous plate secreted by some gastropods and other molluscs, which serves to close the aperture of the shell when the animal is retracted; also, the flap or lid closing the aperture of the shell in sessile cirripeds.
1777Pennant Zool. IV. 61 Lepas..Common English Barnacle,..the lid or operculum sharp pointed. 1777G. Forster Voy. round World I. 434 The round operculum, or cover of a shell. 1856Woodward Mollusca 47 Most spiral shells have an operculum, or lid, with which to close the aperture when they withdraw for shelter. 1866J. G. Murphy Comm. Exod. xxx. 34 Onycha is probably the operculum..or lid of the shell of a strombus.
c. Applied to various other parts and organs covering or closing an aperture: spec.
(a) In aquatic mammalia, as the water-vole, a part of the ear, which acts as a valve to prevent the entrance of water. (b) In birds, the ear-conch or feathered flap of the ear of the owl; also, the nasal scale, a small horny or membranous lid or flap which in some birds closes the nostril. (c) In insects, the covering of each of the two spiracles on the sides of the metathorax. (d) In the king-crab (Limulus), the eighth pair of appendages which are conjoined into a single broad plate covering the succeeding appendages. (e) In spiders, each of the small scales covering the branchial and tracheal stigmata or breathing-orifices. (f) In Chilostomata and some other Polyzoa, the movable lid of the cell of the polypid which is shut down when the zooid is withdrawn within. (g) In Infusoria, as Vorticella, the lid of the lorica or protective sheath.
1713Derham Phys.-Theol. vii. ii. 382 note, This Bottom or Base of the Columella [in the inner ear of a bird], I call the Operculum. Ibid., In the Conclave, at the Side opposite to the Operculum, the tender Part of the Auditory Nerve enters. 1794G. Adams Nat. & Exp. Philos. I. vi. 239 The moveable operculum on the pipe of the human throat, which is imitated by the reed of the organ. 1816Kirby & Sp. Entomol. (1818) II. xxiv. 405 The drum-covers or opercula [of the cicada] from beneath which the sound issues. 1826Ibid. III. 383 Opercula, plates that cover the vocal spiracles in humming insects. 1840Penny Cycl. XVIII. 366/1 Myriapora. Animals cylindrical, terminating anteriorly in a tubular extensible proboscis..; on one side of this body is a cartilaginous round operculum. 1842Ibid. XXIII. 117/2 The aperture of the ear..is large, measuring,..in the Brown Owl, more than an inch in length. This is protected by an operculum. 1843Ibid. XXVII. 629/1 In each half of this operculum [in the king-crab] are to be distinguished one or two basilary pieces and two terminal laminæ. 1888Rolleston & Jackson Anim. Life 234 The mouth so-called.. is crescentic in outline, and its proximal edge or lip is thickened, forming the operculum, a structure from which the suborder Cheilostomata takes its name. Ibid. 523 Limulus has six pairs of limbs on the abdominal mesosoma, of which the first pair fuse to form a genital operculum. 1894Newton Dict. Birds 675 In Asio,..the conch is enormously exaggerated,..and is furnished in its whole length with an operculum. 1897Allbutt's Syst. Med. II. 1017 The shell [of the egg of Bothriocephalus latus] is simple, brown, and closed in at one end with an operculum.
2. Bot.
a. The lid of the capsule in mosses, and of certain circumscissile capsules in phanerogams; also, the lid of the pitcher in Nepenthes, and the concail limb of the calyx of Eucalyptus.
1788Lee Introd. Bot. (ed. 4) Gloss. 422 Operculum, a Cover, as in the Mosses. 1830Lindley Nat. Syst. Bot. 64 In Eucalyptus..the sepals are consolidated into a cup-like lid, called the operculum. 1840Penny Cycl. XVI. 9/2 The urn itself [of mosses] is closed by a lid, or operculum. Ibid. 446/1 Operculum..this term..has also been applied to the lid which covers in the Pitcher of Nepenthes, where it is the lobe of a modified leaf. 1857Berkeley Cryptog. Bot. 483. 1867 J. Hogg Microsc. ii. i. 310 These spore-capsules are closed on their summit by opercula or lids.
b. The lid of the ascus or sporangium of certain fungi.
1879W. Phillips tr. E. Boudier in Grevillea VIII. 46 After the examination of a considerable number of Discomycetes, I am able to call the attention of mycologists to the necessity of separating this family into two very natural sections, according as to whether the mode of dehiscence is with or without an operculum. 1887,1888[see astropyle]. 1971P. H. B. Talbot Princ. Fungal Taxon. xi. 160 Operculate asci have an operculum at the apex: a hinged lid-like opening.
3. Anat. In the brain, the principal covering of the insula or island of Reil, which overlaps the gyri operti from above.
1892Syd. Soc. Lex.
4. gen. A cover. Also fig.
1837Civil Eng. & Arch. Jrnl. I. 58/1 They carry small square bits of black paper, which project in front of the screen, and serve as opercula or covers to conceal the letters. 1866Blackmore Cradock Nowell xxiv. (1883) 116 Noble wine deserves not to be the mere operculum to a stupidly-mixed hot meal. |