Charles Darwin: The Origin of Species by means of Natural Selection

GLOSSARY 1. GLOSSARY OF THE PRINCIPAL SCIENTIFIC TERMS USED IN THE PRESENT VOLUME. (continued)

GANGLION.--A swelling or knot from which nerves are given off as from a centre.

GANOID FISHES.--Fishes covered with peculiar enamelled bony scales. Most of them are extinct.

GERMINAL VESICLE.--A minute vesicle in the eggs of animals, from which the development of the embryo proceeds.

GLACIAL PERIOD.--A period of great cold and of enormous extension of ice upon the surface of the earth. It is believed that glacial periods have occurred repeatedly during the geological history of the earth, but the term is generally applied to the close of the Tertiary epoch, when nearly the whole of Europe was subjected to an arctic climate.

GLAND.--An organ which secretes or separates some peculiar product from the blood or sap of animals or plants.

GLOTTIS.--The opening of the windpipe into the oesophagus or gullet.

GNEISS.--A rock approaching granite in composition, but more or less laminated, and really produced by the alteration of a sedimentary deposit after its consolidation.

GRALLATORES.--The so-called wading-birds (storks, cranes, snipes, etc.), which are generally furnished with long legs, bare of feathers above the heel, and have no membranes between the toes.

GRANITE.--A rock consisting essentially of crystals of felspar and mica in a mass of quartz.

HABITAT.--The locality in which a plant or animal naturally lives.

HEMIPTERA.--An order or sub-order of insects, characterised by the possession of a jointed beak or rostrum, and by having the fore-wings horny in the basal portion and membranous at the extremity, where they cross each other. This group includes the various species of bugs.

HERMAPHRODITE.--Possessing the organs of both sexes.