GLOSSARY- 311 



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 PalEeozoic 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. 



Differentiation. — 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 dissimilar 

 forms. 



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

 viduals. 



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. 

 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. 

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



Fauna. — The totality of the animals naturally inhabiting a certain 

 country or region, or which have lived during a given geological 

 period. 



