GLOSSARY. 313 



history of the earth, but the term is generally applied to the 

 close of the Tertiary epoch, when nearly the whole of Europe 

 was subjected to an arctic climate. 



Gland. — An organ which secretes or separates some peculiar prod- 

 uct 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 sedi- 

 mentary deposit after its consolidation. 



Geallatores. — The so-caUed Wading-birds (Storks, Cranes, Snipes, 

 &e.), 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, characterised by 

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

 fore-wings horny in the basal portion and membranous at the 

 extremity, where they cross each other. This group includes 

 the various species of Bugs. 



Hermaphrodite. — Possessing the organs of both sexes. 



Homology. — That relation between parts which results from their 

 development 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 in- 

 dividual, as in the case of the fore and hind legs in quadrupeds, 

 and the segments or rings and their appendages of which the 

 body of a worm, a centipede, &c., is composed. The latter is 

 called serial homology. The parts which stand in such a rela- 

 tion to each other are said to be homologous, and one such part 

 or organ is called the homologue of the other. In different 

 plants the parts of the flower are homologous, and in general 

 these parts are regarded as homologous with leaves. 



Homoptera. — An order or sub-order of Insects having (like the 

 Hemiptera) a jointed beak, but in which the fore-wings are 

 either wholly membranous or wholly leathery. The Cicadce, 

 Frog-hoppers, and Aphides, are well-known examples. 

 Hybrid. — The offspring of the union of two distinct species. 



