1. The
female reproductive cell which, after fertilization, develops
into a
new member of the
same species (von Baer, 1827), an egg.
2. The
human ovum: a
round cell about 0.1 mm. In diameter, produced in the ovary, where
there is deposited
near it a
noncellular covering (oolemma,
zona pellucida,
zona radiata). It consists of protoplasm which contains some yolk, enclosed by a
thin cell wall (vitelline membrane). There is a
big nucleus (germinal vesicle),
within which is a
nucleolus (germinal spot). By extension, the
word is
also used to identify any
early stage of the conceptus, when the
embryo itself constitutes a tiny and insignificant
part of the whole.
This
entry appears with alow from the Vocabulary of Cell and Molecular Biology