Vitellus

from WordNet (r) 3.0 (2006)

vitellus
    n 1: nutritive material of an ovum stored for the nutrition of
         an embryo (especially the yellow mass of a bird or reptile
         egg) [syn: {yolk}, {vitellus}]

from The Collaborative International Dictionary of English v.0.48

Vitellus \Vi*tel"lus\, n. [L., the yolk of an egg.]
   [1913 Webster]
   1. (Biol.) The contents or substance of the ovum; egg yolk.
      See Illust. of {Ovum}.
      [1913 Webster]

   2. (Bot.) Perisperm in an early condition.
      [1913 Webster]