YOLK

Yolk (yōlk or yōk; 277), n. [[OE. yolke, yelke, ”olke, ”elke, AS. geoloca, geoleca, fr. geolu yellow. See Yellow.]] [Written also yelk.] 1. 1. The yellow part of an egg; the vitellus.
2. 2. (Zoöl.) An oily secretion which naturally covers the wool of sheep.
Yolk cord (Zoöl.), a slender cord or duct which connects the yolk glands with the egg chambers in certain insects, as in the aphids. — Yolk gland (Zoöl.), a special organ which secretes the yolk of the eggs in many turbellarians, and in some other invertebrates. See Illust. of Hermaphrodite in Appendix. — Yolk sack (Anat.), the umbilical vesicle. See under Unbilical.