YOLK or YELK, _n._ “Yellow” of an egg; a soft, opaque, yellow globular
mass, enveloped in a proper membrane (the vitelline) and suspended in
the white by the _chalazæ_. It has a central cavity full of a clear
substance, furnished with a duct leading to a mass of cells termed
_proligerous disc_; adhering to its surface is the _cicatriculum_, or
“tread,” which becomes the embryo.