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)

DEGRADATION.--The wearing down of land by the action of the sea or of meteoric agencies.

DENUDATION.--The wearing away of the surface of the land by water.

DEVONIAN SYSTEM or FORMATION.--A series of Palaeozoic rocks, including the Old Red Sandstone.

DICOTYLEDONS, or DICOTYLEDONOUS PLANTS.--A class of plants characterised by having two seed-leaves, by the formation of new wood between the bark and the old wood (exogenous growth) and by the reticulation of the veins of the leaves. The parts of the flowers are generally in multiples of five.

DIFFERENTATION.--The separation or discrimination of parts or organs which in simpler forms of life are more or less united.

DIMORPHIC.--Having two distinct forms.--DIMORPHISM is the condition of the appearance of the same species under two dissimilar forms.

DIOECIOUS.--Having the organs of the sexes upon distinct individuals.

DIORITE.--A peculiar form of Greenstone.

DORSAL.--Of or belonging to the back.

EDENTATA.--A peculiar order of Quadrupeds, characterised by the absence of at least the middle incisor (front) teeth in both jaws. (Examples, the Sloths and Armadillos.)

ELYTRA.--The hardened fore-wings of Beetles, serving as sheaths for the membranous hind-wings, which constitute the true organs of flight.

EMBRYO.--The young animal undergoing development within the egg or womb.

EMBRYOLOGY.--The study of the development of the embryo.

ENDEMIC.--Peculiar to a given locality.

ENTOMOSTRACA.--A division of the class Crustacea, having all the segments of the body usually distinct, gills attached to the feet or organs of the mouth, and the feet fringed with fine hairs. They are generally of small size.