2. (Biol.) One of the methods by which the various germinal layers of
the ovum are differentiated.
In embolic invagination, one half of the blastosphere is pushed in
towards the other half, producing an embryonic form known as a
gastrula. -- In epibolic invagination, a phenomenon in the development
of some invertebrate ova, the epiblast appears to grow over or around
the hypoblast.
In`va*les"cence (?), n. [L. invalescens, p. pr. of invalescere to
become strong. See 1st In-, and Convalesce.] Strength; health. [Obs.]