Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to Blastula: gastrulation, archenteron


A hollow sphere of cells characteristic of the early metazoan embryo.



a stage in the development of the embryo of multicellular animals culminating in cleavage.

The structure of the embryo in the blastula stage depends on the structure of the egg and type of cleavage. Radial cleavage (echinoderms, lancelets, amphibians, sturgeon) gives rise to a coeloblastula, a spherical embryo with a cavity, or blastocoel, which is filled with a fluid differing in chemical composition from the medium surrounding the embryo. The blastocoel is sometimes in the center of the blastula but is generally shifted to the animal (upper) part of the embryo. The blastular wall, the blastoderm, consists of one, several, or many rows of cells. In animals with the spiral type of cleavage (most mollusks and some worms, for example), the blastula is formed without a cavity, a sterroblastula. Animals with incomplete (partial) discoidal cleavage (bony fishes, sharks, reptiles, birds) form a discoblastula whose cavity is reduced; the upper wall consists of many rows of cells while the lower uncleaved wall contains the yolk. Partial superficial cleavage (some arthropods) gives rise to a blastula in which the cavity is filled with yolk.

Cleavage of eggs in mammals and man ends in the formation of blastocysts rather than blastulas.

References in periodicals archive ?
Besides that, further cleavages into morulla, blastula, gastrula, early prism, 2-and 4-arm pluteus stages showed significant differences (P[?] 0.05) in development times among these four salinity levels.
Parameters (%) Antibody group PBS group 6- to 8-cell stages on the third day 24.8% (114/459) 48.4% (183/378) Blastula stage on the fifth day 26.8% (123/459) 57.1% (216/378) Morula stage on the fifth day 12.4% (57/459) 24.6% (93/378) Parameters (%) Blank control group P value 6- to 8-cell stages on the third day 51.0% (192/376) <0.01 (a,b) Blastula stage on the fifth day 64.9% (244/376) <0.01 (a,b) Morula stage on the fifth day 20.2% (76/376) <0.01 (a,b) The first day referred to the day of embryo collection.
splendens es que la gastrulacion es un fenomeno concomitante a la epibolia que acontece a partir de un grupo de celulas localizadas en el polo animal del huevo telolecito (blastula) y durante la gastrulacion, las celulas de la blastula experimentan una redistribucion dramatica para originar un embrion multilaminar con rudimentos de cabeza, tronco y cola (34), generado a traves de movimientos celulares altamente coordinados mediante los cuales, grupos definidos de celulas se internalizan desde la superficie formando un blastopore y dando origen al endomesodermo (28).
The beginning of gastrula marks the end of the blastula stage, and it is followed by epiboly, defined as the movement of the yolk syncytial layer and blastodisc around the yolk cell.
Until the early blastula stage the embryos continued to be flattened.
similis 6 (9) 2 (6) 6 (14) 23 17 (17) (41) Oncaea borealis 3 (15 2 (0) 28 (6) 11 23 4 (28) (1)) (20) (17) Harpacticoids 0 (1) Unidentified 4 (4) 3 (0) 3 (0) 3 (1) 0 (3) 82 copepods (154) Copepod nauplii 7S (78) 192 553 329 273 138 (285) (457) (373) (391) (309) Zoea larvae Ostracods 1 (0) Decapod 0 (1) Euphausiid 1 (0) Veliger larvae 1 (2) 3 (4) 0 (4) Sagitta elegans 3 (2) 0 (1) 1 (0) 4 (4) 1 (0) Pluteus larvae 0 (2) Blastula larvae Echinoderm juvenile 0 (1) Larvacea 0 (4) 3 (5) 1 (0) 3 (1) 15 (6) 3 (1) Oikopleura 1 (0) Fish larvae Zooplankton Mar 7 Mar 18 May 25 Silicoflagcllates 0 (1) Foraminifera Medusa 0 (2) 0 (2) Polychaetc larvae 3 (5) Calanus finmarchicus 2 (3) 1 (4) Pseudocalanus spp.
turn, inner, entrails, dysentery, industry, blastula, gastrula,
An embryonic blastula stage is a characteristic exclusive to animals.
Our findings of sharp declined of cortisol after fertilization at blastula and gradual increased around the time of hatching has also been documented in the Japanese flounder (de Jesus et al.,1991), milkfish Chanos chanos (Hwang et al.,1992), Lates calcarifer (Sampath-Kumar et al., 1995), gilthead sea bream S.
The phenomenon occurs at the blastula stage, between the 13th and 15th day after fertilization.