PRONUCLEUS

(Lat.), n. m. Pro(pro2)-nu2(nu4)'kle2-u3s(u48). From pro, before, and nucleus (q.v.). Fr., p., pronucleus. Ger., P., Vorkern. A primordial or germinal nucleus; in botany, the nucleus of a conjugating gamete, which by fusion with another p. forms the germ-nucleus. [B, 77, 279 (o, 35).] Female p. Lat., p. fozmininus. Fr., pronucleus (ou noyau) femelle. Ger., Eikern, weiblicher Vorkcrn (oder P.). 1. A small body, lying at first near the periphery, just beneath the extrusion globules, and representing the portion of the nucleus of the ovum (see Germinal VESICLE) which remains after the extrusion of the polar globules. It sinks to or toward the centre of the vitellus. where it usually remains, and must fuse with the male p. before segmentation can take place. A system of radiating lines runs out from it into the yolk, forming a star-like figure (see under ASTER [1st def.]), the so-called female aster. [A, 5; J, 1, 23, 30; Minot, " Am. Nat.," xiv, p. 242 (a, 32).] 2. In botany, the nucleus of the oosphere, which by fusion with the male p. forms the germ-nucleus. [B, 77 (a, 35).] Male p. Lat., p. mosculinus. Fr., pronucleus (ou noyau) mdle. Ger., mdnnlicher Vorkern, Sperm a kern, Hodenkorner. 1. The p. into which the head or some other portion of a sperm a to zooid is transformed after it has imbedded itself in the vitellus and become enlarged, clear, and spheroidal. It finally unites with the female p., and, like the latter, is surrounded by radiating lines forming the so-called male aster. [A, 5; J, 1, 23, 30; Minot, I. c.] 2. In botany, the generative nucleus derived from the pollen-tube, which by fusion with the nucleus of the oosphere, or female nucleus, forms the germ-nucleus. [B, 77 (a, 35).] P. derive (Fr.). Of Van Beneden, the smaller, rounded portion of a clear spot that appears on each of the two spheres formed by the first segmentation of the vitellus, the other portion, larger and surrounding the p. derive, being termed the p. engendre. [A, 15.] P. engendre (Fr.). See under P. derive. Segmentation p. See Gerw-NUCLEUs and Germinal SPOT. Sperm-p. See Male p. [s. 339]