*Germinal Vesicle. A minute vesicle in the eggs of animals, from which the development of the embryo proceeds.
Gravitation (Physics). That species of attraction or force by which all bodies or particles of matter in the universe tend toward each other; called also attraction of gravitation, universal gravitation, and universal gravity.
Gravity (Physics). The tendency of a mass of matter toward a center of attraction; especially the tendency of a body toward the center of the earth, terrestrial gravitation.
Gyrus, pl. Gyri (Anat.). A convolution of the brain.
*Habitat. The locality in which a plant or animal naturally lives.
Heredity. The transmission of the physical and psychical qualities of parents to their offspring; the biological law by which living beings tend to repeat themselves in their descendants.
Homologous. Having the same relative proportion, position, value, or structure; especially—(a) (Geom.) Corresponding in relative position and proportion. (b) (Alg.) Having the same relative proportion or value, as the two antecedents or the two consequents of a proportion. (c) (Chem.) Being of the same chemical type or series; differing by a multiple or arithmetical ratio in certain constituents, while the physical qualities are wholly analogous, with small relative differences, as if corresponding to a series of parallels; as, the species in the group of alcohols are said to be homologous. (d) (Zoöl.) Being of the same typical structure; having like relations to a fundamental type of structure; as, those bones in the hand of man and the fore-foot of a horse are homologous that correspond in their structural relations—that is, in their relations to the type-structure of the fore-limb in vertebrates.
Homology. That relation between parts which results from their development from corresponding embryonic parts, either in different animals, as in the case of the arm of a man, the fore-leg of a quadruped, and the wing of a bird; or in the same individual, as in the case of the fore and hind legs in quadrupeds, and the segments or rings and their appendages of which the body of a worm, a centiped, etc., is composed. The latter is called serial homology. The parts which stand in such a relation to each other are said to be homologous, and one such part or organ is called the homologue of the other. In different plants the parts of the flower are homologous, and in general these parts are regarded as homologous with leaves.
Hypothesis. 1. A supposition; a proposition or principle which is supposed or taken for granted, in order to draw a conclusion or inference for proof of the point in question; something not proved, but assumed for the purpose of argument.
2. A system or theory imagined or assumed to account for known facts or phenomena.