|a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.|
|an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle.|
|—n , pl -las, -lae|
|ectoderm mesoderm See also endoderm a saclike animal embryo consisting of three layers of cells (ectoderm, mesoderm, and endoderm) surrounding a central cavity (archenteron) with a small opening (blastopore) to the exterior|
|[C19: New Latin: little stomach, from Greek gastēr belly]|
gastrula gas·tru·la (gās'trə-lə)
n. pl. gas·tru·las or gas·tru·lae (-lē')
An embryo at the stage following the blastula, consisting of a hollow, two-layered sac of ectoderm and endoderm surrounding an archenteron that communicates with the exterior through the blastopore.
|gastrula (gās'trə-lə) Pronunciation Key
Plural gastrulas or gastrulae (gās'trə-lē')
An animal embryo at the stage following the blastula. The gastrula develops from the blastula by invagination (inpocketing), forming an inner cavity with an opening and causing the cells to be distributed into an outer layer (ectoderm) and an inner layer (endoderm). In complex animals such as vertebrates, a third layer (mesoderm) also forms. These layers later develop into the organs and tissues of the body. In vertebrates and other deuterostomes, the opening of the gastrula becomes the anus, while in protostomes (such as arthropods), it becomes the mouth. ◇ The development of an embryo from blastula to gastrula is called gastrulation. Compare blastula.
early multicellular embryo, composed of two or more germinal layers of cells from which the various organs later derive. The gastrula develops from the hollow, single-layered ball of cells called a blastula which itself is the product of the repeated cell division, or cleavage, of a fertilized egg. This cleavage is followed by a period of development in which the most significant events are movements of cells relative to one another.
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