GLOSSARY. 311 



Uegbidation. — 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 Palseozoic rocks, in- 

 cluding 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. 



Difpeeentiation. — 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 con- 

 dition of the appearance of the same species under two dis- 

 similar forms. 



Dkecious. — Having the organs of the sexes upon distinct indi- 

 viduals. 



DiOBiTE. — A peculiar form of Greenstone. 



DoBSAL. — 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.) 

 Elttea. — 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 



ege or womb. 

 Embryology.— The study of the development of the embryo. 

 Endemic. — Peculiar to a given locality. 

 Entomosteaca. — 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. 

 Eocene.— 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. 

 Ephembrous Insects.— Insects allied to the May-fly. 



