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An opening at either end of the embryonic neural canal.

An embryo or certain invertebrates in the stage when the primitive band is first developed.

astic cartilagelike rod which is developed beneath the medullary groove in the vertebrate embryo, and constitutes the primitive axial skeleton around which the centra of the vertebræ and the posterior part of the base of the skull are developed; the chorda dorsalis. See Illust. of Ectoderm.

Having the radicle of the embryo lying against the back of one of the cotyledons; incumbent.

An analogous mass of protoplasm in the ovule of a flowering plant; an embryonic vesicle. Goodale.

one tissue; the residue after removal of the mineral matters from bone by dilute acid; in embryonic tissue, the substance in which the mineral salts are deposited to form bone; -- called also ostein. Chemically it is the same as collagen.

simple auditory organs of many invertebrates, containing a fluid and otoliths; also, the embryonic vesicle from which the parts of the internal ear of vertebrates are developed.

The old theory that the egg contains the whole embryo of the future organism and the germs of all subsequent offsprings and is merely awakened to activity by the spermatozoön; -- opposed to spermism or animalculism.

A portion of the mesoblast (of peripheral origin) of the developing embryo, the cells of which are especially concerned in forming the first blood and blood vessels. C. S. Minot.

on of seed without fertilization, believed to occur through the nonsexual formation of an embryo extraneous to the embrionic vesicle.

The albumen of a seed, especially that portion which is formed outside of the embryo sac. -- Per`i*sper"mic, a.

The penis or clitoris, or the embryonic or primitive organ from which either may be derived.

A young plant, or plant in embryo. E. Darwin.

The embryo which has begun its development in the act of germination.

In embryonic development, a vesicle filled with fluid, formed from the morula by the divergence of its cells in such a manner as to give rise to a central space, around which the cells arrange themselves as an envelope; an embryonic form intermediate between the morula and gastrula. Sometimes used as synonymous with ga…

The first bud, or gemmule, of a young plant; the bud, or growing point, of the embryo, above the cotyledons. See Illust. of Radicle. Gray.

The theory that living organisms originate in cells or embryos of different kinds, instead of coming from a single cell; -- opposed to monogenesis.

extending around the end of the vertebral column, like that which is first formed in the embryo of fishes; diphycercal.

The embryonic shell, or first chamber, of ammonites and other cephalopods.

One of the primitive masses, or segments, into which the mesoblast of the vertebrate embryo breaks up on either side of the anterior part of the notochord; a mesoblastic, or protovertebral, somite. See Illust. of Ectoderm.