—yolked, adj. —yolkless, adj. —yolky, adj./yohk, yohlk/, n.1. the yellow and principal substance of an egg, as distinguished from the white.2. Embryol. the part of the contents of the egg of an animal that enters directly into the formation of the embryo, together with any material that nourishes the embryo during its formation.3. the essential part; the inner core.4. a natural grease exuded from the skin of sheep.Also, yoke.[bef. 1000; ME yolke, yelke, OE geoloca, deriv. of geolu YELLOW]
* * *also called Deutoplasm,the nutritive material of an egg, used as food by a developing, embryonic animal. Eggs with relatively little, uniformly distributed yolk are termed isolecithal. This condition occurs in invertebrates and in all but the lowest mammals. Eggs with abundant yolk concentrated in one hemisphere of the egg are termed telolecithal. This occurs in many invertebrates and in all vertebrates lower than marsupial mammals. In arthropods, the yolk is massed near the centre of the egg; such eggs are termed centrolecithal.
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