Forms: α. 1 ʓeolca, ʓeoloca, ʓioleca, 3 ȝeolke, 4 yholk(e, 4–5 ȝolke, 5 ȝolk, 7 yeolke, yolke, yowlk, yoalk(e, 8– Sc. yowk, (9 yoke), 7– yolk. β. 4–5 ȝelke, 4–7 yelke, 5 ȝelk, 7 yealk, 6– yelk. [OE. ʓeolca, ʓeoleca, -oca, f. ʓeolu yellow.
The spelling yelk appears to have ceased to be frequent since the third quarter of the 19th century, but it is found in recent scientific and technical works. The pronunciation (yelk) survives locally; it is not clear during what period or to what extent it has been current in standard English.]
1. The yellow internal part of an egg, surrounded by the ‘white’ or albumen, and serving as nourishment for the young before it is hatched.
α. a. 1000. Boeth. Metr., xx. 170. Þæm anlicost þe on æʓe bið ʓioleca onmiddan.
c. 1000. Sax. Leechd., II. 38. Hænne æʓes ʓeolocan.
c. 1000. Ælfric, Hom., I. 40. Sceawa nu on anum æʓe, hu þæt hwite ne bið ʓemenged to ðam ʓeolcan.
c. 1290. St. Michael, 635, in S. Eng. Leg., 317. Ase þe ȝwyte of þe Eye goth a-boute þe ȝeolke.
c. 1340. Richard Rolle of Hampole, Prick of Conscience, 6446. An egge yholke.
1398. Trevisa, Barth. De P. R., XII. xix. (Bodl. MS.). Þe chiken is ibred of þe white and ynorissched wiþ þe ȝolke.
c. 1420. Liber Cocorum (1862), 18. Take ȝolkes of eyren þat harde bene.
1486. Bk. St. Albans, b vj b. Tempere it with clere wyne and with the yolke of an egge.
1604. Marston, Malcontent, II. iv. D 1 b. Seauen and thirty yowlks of Barbarie hennes eggs.
1605. Timme, Quersit., I. xiv. 67. The yeolke of the egge … is the true sulphur.
1666. Third Adv. to Painter, 18. An Addle-egg with double Yoalk.
a. 1756. Mrs. Haywood, New Present for Maid (1771), 158. Beat up the yolks of three eggs.
1842. Tennyson, Audley Court, 24. A pasty costly-made, Where quail and pigeon, lark and leveret lay,… with golden yolks Imbedded and injellied.
β. c. 1325. Gloss. W. de Bibbesw., in Wright, Voc., 150. Le moiel, a yelke.
c. 1400. Lanfranc’s Cirurg., I. iii. 53. Wiþinne þe wounde leie þe ȝelke of an ey.
1560. Whitehorne, Ord. Souldiours (1588), 46 b. Oile of the yelkes of egges.
1600. Surflet, Country Farm, VII. lxv. 895. Putting thereto the yelkes of two egs and a little saffron.
a. 1625. Fletcher, Wife for Month, II. i. Like to poch’d eggs That had the yelks suckt out.
1650. Sir T. Browne, Pseud. Ep., III. xxviii. (ed. 2), 150. That a Chicken is formed out of the yelk of the egge,… the people still opinion.
a. 1700. Evelyn, Diary, 29 Sept. 1645. He abounded in things petrified, wallnuts, eggs in which ye yealk rattl’d.
1756. C. Lucas, Ess. Waters, I. 73. [These] divided and inviscated by the yelk of an egg become miscible in … water.
1864. Reader, 5 Nov., 572/2. The embryos of man [etc.] are nourished … by the mother’s blood,… and those of birds by the yelk of the egg.
1884. Health Exhib. Catal., 39. The leather is … soaked in liquor made of the yelks of eggs.
b. in Biol. extended to the corresponding part in any animal ovum, which serves for the nutrition of the embryo (nutritive or food-yolk), and to the protoplasmic substance from which the embryo is developed (formative or germ-yolk): = VITELLUS 1.
1835–6. [see 5].
1851. Woodward, Mollusca, 51. After impregnation, the germinal vesicle, which then subsides into the centre of the yolk, divides spontaneously into two.
1879. Haeckel’s Evol. Man, I. ii. 28. Cephalopods, the embryo of which has a bag of yelk protruding from the mouth.
1889. Geddes & Thomson, Evol. Sex, viii. 101. The yolk … is more or less readily distinguished from what is often called the formative protoplasm.
c. 1909. E. Ray Lankester, Science fr. Easy Chair, xxii. 209. The ‘yelk’ of the bird’s egg … corresponds to the black sphere of the frog’s egg—the actual germ.
c. Bot. = VITELLUS 2. Obs. rare.
1807. J. E. Smith, Phys. Bot., xix. (1814), 222. Vitellus, the Yolk, first named and fully illustrated by Gaertner.
† 2. fig. Center; innermost part, ‘core’; also, best part.
1387–8. T. Usk, Test. Love, III. iv. (Skeat), l. 198. Of loue (quod she) wol I nowe ensample make, sithen I knowe the heed knotte in that yelke.
1614. T. Gentleman, England’s Way, 12. Then being the very heart of Summer, and the very yoalke of all the yeare.
1637. Rutherford, Lett. to Parishioners, 13 July. Christ hath the yolke and heart of my love. Ibid. (1637), Lett. to J. Kennedy, Lett. (1664), 187. Then Christ would … conquer to himself a lodging in the inmost yolk of our heart.
1695. J. Sage, Fund. Charter Presbyt., Pref., Wks. 1844, I. 32. The true yolk of the mystery.
c. 1730. Ramsay, To Duncan Forbes, iv. Chance gi’es them of gear the yowk, And better chiels the shell.
3. (Also y. of egg.) Name for a gastropod mollusk of the genus Nerita, from the appearance of its shell.
1796. Nemnich, Polygl.-Lex., 945. Yolk nerita, nerita vitellus and albumen.
1815. S. Brookes, Introd. Conchol., 157. Yolk of Egg, Nerita Vitellus.
4. a. A rounded opaque or semi-opaque part occurring in window-glass; also, a pane of rough or thick glass. b. A hard or otherwise differentiated nodule in stone, rock, etc. local.
1808. Jamieson, s.v. Those round, opaque and radiated crystallizations, which are found in window-glass, in consequence of being too slowly cooled, are generally termed yolks in S[cotland].
1811. Acc. Game Curling, 3. Those whinstone nodules … called yolks, on account of their toughness.
1883. Simmonds, Dict. Trade, Suppl. Yolk, a local name in the Forest of Dean for masses of rotten stone intervening in the grey stone.
1886. J. Barrowman, Sc. Mining Terms, 74. Yolk coal, or Yolks, free or soft coal.
1901. W. Laidlaw, Poetry & Prose, 34. They [sc. windows] were of yolks of darkish green, Sae dim they didna need a screen.
5. attrib. and Comb. in sense 1 b.
The most important are: yolk-bag, -sac, the sac or vesicle inclosing the yolk, esp. when attached to the umbilicus as an organ of nutrition; it is connected with the intestine of the embryo by the yolk-duct or yolk-stalk; yolk-cleavage, -division, -segmentation, the division of the (formative) yolk as the initial process in the development of the embryo; yolk-membrane, -skin, the delicate membrane surrounding the yolk of some ova.
1835–6. Todd’s Cycl. Anat., I. 560/2. The point of attachment of the yolk-bag [in the Cephalopod], which is suspended from the head of the embryo. Ibid. (1849–51), IV. 1223/2. The central yolk-mass of the body.
1857. Gosse, Omphalos, xi. 330. The yelk-globe, fastened by its twisted chalazæ, is suspended in a glairy fluid (albumen).
1859. Todd’s Cycl. Anat., V. 46/1. The process of yolk-segmentation. Ibid., 51/2. The ovum of the frog … consists of the yolk-ball,… surrounded by a … layer of … albuminous matter. Ibid. [124/1]. The germ-forming and yolk-forming portions.
1861. J. R. Greene, Man. Anim. Kingd., Cælent., 15. Many ova are provided with an outer envelope, known as the yolk-sac or ‘vitelline membrane.’ Ibid. After fecundation, the ovum exhibits a series of changes inaugurated by the process of ‘segmentation’ or yolk-division. Ibid., 181. After yolk-cleavage the embryo appears rudely cylindrical in form.
1878. Bell, trans. Gegenbaur’s Comp. Anat., 18. Special particles—yolk-granules—may appear in its protoplasm. Ibid., 53. Special glands, Yolk glands, are formed from the ovary.
1879. Haeckel’s Evol. Man, I. x. 284. Connected with the central portion of the intestinal tube by a thin stalk, the yelk-duct.
1888. Goode, Amer. Fishes, 190. The comparatively large yelk-sac.
1889. Rolleston & Jackson, Anim. Life, Introd. p. xxvii. The Gastrula is derived either by invagination or by differentiation of the yolk cells.
1898. P. Manson, Trop. Diseases, xxxvi. 532. The points to be attended to in the diagnosis of ova are size, shape, colour … the presence or otherwise of yolk spheres.
1900. Q. Jrnl. Microsc. Sci., Feb., 7. The thin … yolk-stalk carrying the vitelline artery.
