Germ

(jerm). In biology, (a) a portion of matter potentially vital and having within itself the tendency to a ume a definite living form (Harvey); a spore, a seed, an embryo, (b) A microbe or bacterium. G.-area, the germinal area, the germinal disc, area germinativa, the spot on an ovum where the development of the embryo begins. G., Asexual, or Unisexual. See Parthenogenesis , Germ-plasm, Evolution, and Reproduction. G.-band, in embryology, one of the bands that unite to form the primitive streak. G.-cell. I. The germinal vesicle in a non-fertilized ovum. 2. The ovum that has been impregnated, but which is still a single cell; a cytula, or a blastomere; a simple sphere. See also Heredity . G., Dentinal, a tooth-papilla, or tooth-pulp. G. of Disease, the special virus or spore through which a disease becomes communicable. G.disc. See G.-area. G. Epithelium, cylindric cells on the surface of the median plate of the mesoblast. G. -flesh. See Sarcophyte. G. -gland, a germ-producing gland; an ovary or a testicle. G. -history, ontogeny, a. v. G. -layer, in biology, any one of the membranes ofa developing germ, as the blastophylla, epiblast, mesoblast, hypoblast, endoderm, ectoderm, mesoderm, somatopleure, splanchnopleure. G. -plasm, in biology, a term introduced by Wei mann to indicate the reproductive or hereditary substance of living organisms. It is held to contain all the primary constituents of the entire organism; it is never produced neo genetically, but is ever pa ed on from the germ-cell in whicli an organism originates in direct continuity to the germ cells of succeeding generations. It causes the production of the new individual by directing the pi of division in ontogeny, in the course of which it becomes changed in a regular manner. It is composed primarily of biophores (a. v.) or bearers of vitality, the smallest units that exhibit vital force. (Cf. pan of De Vries, physiologic units of Herbert Spencer, plastidules of Elsberg, and plasomes of Wiesner.) These biophores unite into groups called determinants (q. v.), each of which is a primary constituent of a cell. Groups of determinants in turn combine to form ids (Cf. ancestral germ-plasms), which correspond to the small granules hitherto called micro-somata (q.v.). The ids again form groups called idants (q. v.), which correspond with the chroma to so mes (q.v.) or rod-like granular ma es of chromatin in the nucleus.