embryo, embrio, embrion, embryon

& a. [Fr. embryon; Lat. embryon; Gr. embryon, from em = en =in, and bryon, neut. of bryon = swelling, full of a thing, pr. par. of bryō =to be full of a thing, to swoll.] A. As substantive: I. Ordinary Language : 1. Lit .: In the same sense as II. 1. "When the crude embryo careful nature breeds, See how she works, and how her work proceeds." Black more: Creation. 2. Fig .: A rudimentary, crude, or undeveloped state; in the first or earliest stages. "The company little expected what a noble work I had then in embryo."-Swift. II. Physiology : 1. Human Phys.: The first beginning of the ani. mal development, not born and still unfinished, The germs of two new cells are first deposited within the ovulum (q. v.) by spontaneous movement. They occupy only the pellucid center of the germinal spot at first, but speedily increase in size, and develop new cells in their own interior, until they alone fill the whole germinal vesicle. Each gives birth to a new generation of two, making four, then eight cells, sixteen, and so on, doubling progre ively, until a mulberry-like ma is produced of innumerable cells. This in the animal embryo moves up to the side of the yolk, flattening against its lining membrane, in contact with the yolk-bag. A second and third layer is then formed from the center within the first ma of cells. The whole is known as the germinal membrane; the external pellicle is called the serous layer, the internal the mucous layer, and the middle the vascular layer, giving rise to the first ve els of the embryonic structure. Thus the beginning of the embryo is a sac, inclosing the nutriment prepared for it prior to the permanent portion to be evolved from the center of this mulberry-ma . The greater portion is then cast off, and nearly all the permanent em bryonic formation is derived from one large cell, at first in the center, but ultimately at the surface of the ma , when it undergoes the flattening described. This, with the cluster of cells round it, forms the germ-spot, with a round transparent space in it, the area pellucid a. The nucleus of this cell is first annular, then pear-shaped, then violin-like, being two long, parallel lines, with a narrow space between them, but separating to inclose a wider space at one end. This is called the Primitive Trace. The parts first formed from this are the spine and spinal-cord (q. v.). Ve els at the same 1633 time are being formed within the substance of the germinal membrane, forming a network known as the Vascular Area, and terminating in the embryo, at the point afterward becoming the umbilicus (q. v.), in two large trunks. The formation of the heart takes place in the vascular layer, and at the same time the production of a digestive cavity begins by the separation of a small part of emendals ěm-bry-on, s. & a. [EMBRYO.]