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The stage of development in animals in which the endoderm is formed and invagination of the blastula has occurred.



one of the stages of embryonic development in multicellular animals. In the gastrula stage the embryo has a two-layer wall and cavity (gastrocoel) that communicates with the surrounding environment by means of an opening, the blastopore. The outer wall is called the ectoderm; the inner wall, the endoderm. They are the primordial embryonic layers. In the beginning the endoderm, and less frequently the ectoderm, also contains the material for a middle layer of tissue—the mesoderm. At the end of gastrulation, the mesoderm separates and becomes independent, and the embryo is transformed from a two-layer to a three-layer organization.

The transformation from the blastula to the gastrula takes place differently in different animals. Already at the gastrula stage, certain differences in the properties of the embryonic layers that are precursors of their morphological differentiation can be observed. The differences in structure of the embryos of different animals at this stage of development are determined both by the structure of the eggs and by the different modes of existence of the embryos. In most animals the embryo spends the gastrula stage in the egg envelope or in the mother’s body; in some hydrozoans the gastrula is a free-living larva. Sometimes the differences pertain to the most general features; for example, in the embryos of bony fish the gastrocoel is lacking, and in certain coelenterate gastrulae the blastopore is lacking. The presence of the gastrula stage (with its characteristic separation into embryonic tissues) in the development of all multicellular organisms was demonstrated by A. O. Kovalevskii and E. Metchnikoff and provided proof of the common origin of animals.


References in periodicals archive ?
After the incubation, gastrulae were liberated from the jelly coat and egg capsules by finely mincing the egg strands with a razor blade.
The ectoderm of 4-day-old gastrulae had "pits," or invaginations (Fig.
Usherin is expressed in gastrulae, planulae, and polyps
Using methods identical to those employed to collect the data illustrated in Figure 4, additional experiments (total n = 7) were conducted on different batches (gametes from different parents) of blastulae, gastrulae, and larvae of S.
The gastrulae developed into bipinnaria-like larvae 36 h after insemination.
Costs of protein synthesis were further examined in cohorts of gastrulae of different ages and parents from those used to test the potential concentration dependency of anisomycin on costs of protein synthesis (Fig.
Early gastrulae show an enlarged blastopore whose aperture progressively reduces in older gastrulae (compare Fig.
The results suggest that DM-1 is expressed in gastrulae and neurulae and in the neural complex and that sea squirt DM-2 is more broadly distributed throughout larval development.