Segmentation of egg: the division of the originally single celled egg into a number of coherent cells or blastomeres; = cleavage.
"Explanation of Terms Used in Entomology" by John. B. Smith
In these cases of injured and isolated blastomeres we have, it seems to me, a plausible theory for the etiology of single terata.
"Essays In Pastoral Medicine" by Austin ÓMalley