| 释义 |
hydroid, a., n.|ˈhaɪdrɔɪd|
[f. hydra 6 + -oid.]
A. adj. Zool. Resembling or allied to the genus hydra of Hydrozoa.
a. Belonging to the order or subclass Hydroidea, of which Hydra is the typical genus.
b. Of the nature of a hydroid (see B. b): opposed to medusoid.
1864in Webster. 1867J. Hogg Microsc. i. iii. 227 Hydroid zoophytes with expanded tentacles. 1877Huxley Anat. Inv. Anim. iii. 132 Some medusoids..the hydroid stages of which are not..known. 1888Rolleston & Jackson Anim. Life 746 Colonies containing polymorphic hydroid individuals, and generally medusoid as well.
B. n.
1. Zool.
a. A Hydrozoan belonging to the Hydroidea.
b. One of the two forms of zooids occurring in Hydrozoa, resembling Hydra in structure, but typically asexual: opposed to Medusa.
1865E. & A. Agassiz Seaside Stud. Nat. Hist. 21 Below these [Ctenophorae and Discophorae] come the Hydroids, embracing the most minute..of all these animals. 1880Libr. Univ. Knowl. I. 332 The fixed hydroids and swimming jelly-fishes are alternate forms assumed by the successive generations of the same animal. 1888Rolleston & Jackson Anim. Life 745 The Hydroid is (1) a permanent locomotor sexual form, multiplying by gemmation, but only temporarily colonial,—Hydra: (2) a larval form which passes by a metamorphosis into a Medusa: (3) a non-sexual but permanent form, sometimes solitary, usually however multiplying by gemmation..giving origin to colonies: (4) a locomotor sexual form..never multiplying by gemmation.
2. Bot. [a. G. hydroid (H. Potonié 1883, in Jahrb. K. Bot. Gartens Berlin II. 243).] An element forming part of the hydrome tissue of a plant.
1887W. Hillhouse tr. Strasburger's Handbk. Pract. Bot. v. 58 The perfect wood-cells..consist only of dead cell-walls, and, as..they simulate the tracheæ, i.e. vessels, they are known as tracheïdes, more recently as hydroïdes. 1968Bell & Woodcock Diversity Green Plants iv. 126 Surrounding a core of tracheid-like cells (sclereids), containing scattered thin-walled cells (hydroids), is a zone of cells conspicuously large in transverse section. 1971E. V. Watson Struct. & Life Bryophytes (ed. 3) ix. 126 Collectively these tissues are known as hadrom and leptom (analogues respectively of xylem and phloem) but the constituent elements are conveniently termed hydroids and leptoids. |