(n.) That stage in the development of the ovum in which the outer cells of the morula become more defined and form the blastoderm.

Anlage Euglena adenovirus aerobe aerobic bacteria amoeba anaerobe anaerobic bacteria animalcule bacillus bacteria bacterium base basis beginning blastula bud bug coccus colon bacillus diatom disease-producing microorganism dyad echovirus egg embryo enterovirus fetus filterable virus flagellate fount fungus germen gram-negative bacteria gram-positive bacteria larva loins microbe microorganism microspore microzoa mold monad nematode nonfilterable virus nucleus nymph origin ovum paramecium pathogen picornavirus protozoa protozoon reovirus rhinovirus rickettsia root rudiment salmonella saprophyte seed source spark spermatozoon spirillum spirochete spore sporozoon staphylococcus start streptococcus tetrad triad trypanosome vibrio virus volvox vorticellum zoospore zygote