cleavage : Idioms & Phrases

cleavage parallel to the base of a crystal, or to the plane of the lateral axes.

noun the fluid-filled cavity inside a blastula
blastocoel; segmentation cavity; blastocele; blastocoele.

(Biol.), a process of cleavage or segmentation, by which the egg undergoes endogenous division with formation of a mass of nearly similar cells, from the growth and differentiation of which the new organism is ultimately formed. See Segmentation of the ovum, under Segmentation.

noun the fissure between the labia majora
pudendal slit; rima pudendi; vulvar slit; rima vulvae; pudendal cleft; urogenital cleft.

(Biol.), the process by which the embryos of all the higher plants and animals are derived from the germ cell. In the simplest case, that of small ova destitute of food yolk, the ovum or egg divides into two similar halves or segments (blastomeres), each of these again divides into two, and so on, thus giving rise to a mass of cells (mulberry mass, or morula), all equal and similar, from the growth and development of which the future animal is to be formed. This constitutes regular segmentation. Quite frequently, however, the equality and regularity of cleavage is interfered with by the presence of food yolk, from which results unequal segmentation. See Holoblastic, Meroblastic, Alecithal, Centrolecithal, Ectolecithal, and Ovum.

(Min.), cleavage, as of rocks, into thin leaves or plates, like those of slate; applied especially to those cases in which the planes of cleavage are not parallel to the planes of stratification. It is now believed to be caused by the compression which the strata have undergone.