458 THE ORIGIN OF SPECIES 



Fungi (sing. Fungus). — A class of cellular plants, of which Mush- 

 rooms, Toadstools, and Moulds are familiar examples. 



FuRCULA. — The forked bone formed by the union of the collar-bones 

 in many birds, such as the common Fowl. 



Gallinaceous Birds. — An order of Birds of which the common 

 Fowl, Turkey, and Pheasant are well-known examples. 



Gallus. — The genus of birds which includes the common Fowl. 



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 Ter- 

 tiary 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, characterized by the 

 possession of a jointed beak or rostrum, and by having the fore- 

 wings horny in the basal portion and membraneous at the ex- 

 tremity, where they cross each other. This group includes the 

 various species of Bugs. 



Hermaphrodite. — Possessing the organ of both sexes. 



Homology. — The relation between parts which results from their de- 

 velopment from corresponding embryonic parts, either in different 

 animals, as in the case of the arm of man, the fore-leg of a 

 quadruped, and the wing of a bird; or in the same individual, as 



