Page:Origin of Species 1872.djvu/455

 .—The wearing away of the surface of the land by water.

or formation.—A series of Palæozoic rocks, including the Old Red Sandstone.

.—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.

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

.—Having two distinct forms.- Dimorphism is the condition of the appearance of the same species under two dissimilar forms.

.—Having the organs of the sexes upon distinct individuals.

.—A peculiar form of greenstone.

.—Of or belonging to the back.

.—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.)

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

.—The young animal undergoing development within the egg or womb.

.—The study of the development of the embryo.

.—Peculiar to a given locality.

.—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.

.—The earliest of the three divisions of the Tertiary epoch of geologists. Rocks of this age contain a small proportion of shells identical with species now living.

.—Insects allied to the May-fly.

.—The totality of the animals naturally inhabiting a certain country or region, or which have lived during a given geological period.

.—The Cat-family.

.—Having become wild from a state of cultivation or domestication.

.—The totality of the plants growing naturally in a country, or during a given geological period.

.—Flowers imperfectly developed in some respects, and collected into a dense spike or head, as in the Grasses, the Dandelion, &c.

.—Of or belonging to the fœtus, or embryo in course of development.

.—A class of animals of very low organisation, and generally of small size, having a jellylike body, from the surface of which delicate filaments can be given off and retracted for the prehension of external objects, and having a calcareous or sandy shell, usually divided into chambers, and perforated with small apertures.