_Gallium._ A metallic element. Symbol: Ga. _Gamete._ A sexual cell which unites with another for reproduction. _Gamma rays._ Becquerel rays which are more penetrating than beta rays and are not deflected by electricity. Equivalent or analogous to X-rays. _Ganglion._ An enlargement of the nerve from which nerve-fibers radiate. _Gas._ A fluid which tends to occupy the whole volume of any vessel in which it is placed. _Gastropoda._ A class of mollusks including the snails. _Geld._ Castrate. _Generalization._ A universal assertion, a principle applying not to any single fact but rather to a large number. A general notion. _Genetics._ The study of heredity and of the beginning of variation. _Genital._ Pertaining to reproduction and the sexual organs. _Genus._ In logic, a class which is divided into sub-classes. In biology, a class of animals usually containing several species. A single genus may in some cases make up a genus of its own, if it appears not to be closely related to any other genus. Plural: genera. The next higher group is the family. _Geo-._ In combinations, earth——. _Geography._ The study of the earth, especially as the environment of man. _Geology._ The study of the crust of the earth. _Germ._ A portion of an organism capable of becoming a new one. Seed, microörganism. Popularly, a germ is a bacterium which causes disease. _Germanium._ A metallic element. Symbol: Ge. _Glacier._ A slowly-moving mass of ice formed by the accumulation of snow on high ground. _Gland._ An organ which secretes constituents of the blood. Secreting cell or cells in plants. _Glans._ The body at the end of the penis and clitoris. _Glass._ A substance made by mixing silicates and including some alkali silicate. Not every sort of glass is transparent. _Glomerate._ Gathered in a compact group. _Glottis._ The opening at the upper end of the windpipe. _Glucinum_ or _beryllium_. A metallic element. Symbol: Gl or Be. _Glucose._ One of a group of sugars, including grape sugar. _Gneiss._ A sort of highly crystalline rock arranged in layers, as of quartz and mica. _Gold._ A metallic element. Symbol: Au. _Gram._ The unit of weight in the metric system. About the weight of a cubic centimeter of water at its greatest density. _Graph._ A symbolical diagram, as in mathematics of chemistry. _Gravity_ or _gravitation_. The attraction existing between bodies. If the earth draws a falling apple, it is said that the apple also draws the earth to it. _Gregarious._ Living in or pertaining to flocks, groups, or communities. Social. _Gymnosperm._ A plant whose seeds are not enclosed in seed-vessels. _Habit._ An action pattern; specifically, one that has been acquired. In biology, a mode of growth. _Hallucination._ The perception of something which is not actually present. _Hardness._ The presence of certain salts in water. _Heat._ Energy which can be transmitted by conduction or radiation, and which is expressed in molecular motion.