| 释义 |
▪ I. ‖ pleon1 Zool.|ˈpliːən|
[Arbitrarily f. Gr. πλέων, pr. pple. of πλεῖν to swim, sail: cf. pereion.]
A name for the abdomen in Crustacea, as bearing the swimming limbs (see pleopod). Also applied by Owen to the tail-spine or telson in the king-crab, etc., considered as representing the abdomen.
1855C. Spence Bate in Rep. Brit. Assoc. (1856) 27 Abdominal segments (or pleon). (Note), From πλέω, navigo: pleon, part which supports the swimming legs. 1873Owen Anat. King Crab 9 The tail-spine (‘pleon’ and ‘telson’..) nearly equals in length the two antecedent divisions. Ibid. 44 In the development of Limulus, the pleon or tail-spine (= pygidium) was the last to appear. 1888Challenger Rep. XXIX. i. 652 The feeble structure of the mouth-organs and of the after-part of the pleon.
Hence ˈpleonal, ˈpleonic adjs., pertaining to the pleon (in quots. the telson of the king-crab).
1873Owen Anat. King Crab 26 The posterior or ‘pleonic’ artery..has more definite tunics and holds a longer course. Ibid. 48 Pleonic plexus..Pleonic artery..Pleonal nerve, or continuation of neural cord.
▪ II. pleon2 Bot.|ˈpliːən|
[a. Gr. πλέον, -ων, neuter of πλέος, -ως full: cf. L. plenum.]
A term proposed by Nägeli for an aggregate of molecules which cannot be increased or diminished in size, without changing its chemical nature.
1882Vines Sachs' Bot. 664 note 1 It will be noted that the Atom, Molecule, and Pleon are chemical ideas, whereas the Micella and Micellar Aggregate are purely physical. 1885G. L. Goodale Physiol. Bot. (1892) 212 The terminology now proposed by Nägeli applies the word pleon to those aggregates of molecules which cannot be increased or diminished without changing their chemical nature. |