American Heritage Dictionary
(1)
Century Dictionary
(2)
GNU Webster's 1913
(1)
WordNet
(1)
Elsewhere on the web
Our eggs don't seem to have much, if any, spatial information initially, and all of the cells in the early blastula are mostly equivalent.— Pharyngula
If we say that a blastula is a human being, I can't even imagine the scale of the tragedy we've engendered just by attempting to bring new life into the world.— Charlottesville Blogs
A blastula is an embryo in the early stage of development.— The Earth Times Online Newspaper
(B) Fate map of blastula-mesenchyme blastula stage embryo.— PLoS Biology: New Articles
Consequently the expression in the blastula is restricted to subgroups of cells without clear orientation (figure 2B).— PLoS ONE Alerts: New Articles

American Heritage Dictionary (1)
Century Dictionary (1)
Bubble size: how much this word was used in a year
Bubble height: used more or less than expected, vs. all uses evenly distributed
You can expect to see this word about once a year.