GLOSSARY 567 



gamete (gSm' et). A germ cell; adj., gametic (ga met' Ik). 



gametogenesis (g:\m e to jen' e sis). The stages in tlie development of a germ cell, or 



reproductive cell, 

 ganglion (gflri' gll 6n). A circumscribed group of nerve-cell bodies; adj., ganglionic 



(ga/i gll 6n' ik). 

 gastr (gtls't'r). G.; stomach. Gastral. Stomach-like. Gastric. Pertaining to 



the stomach, 

 gastrovascular (gfts tro vfts' ku lar) cavity. A cavity in the lower Metazoa which 



serves for both digestion and distribution of food. 

 gastrula (gfts' troo la). A stage in embryogeny when the embryo has two layers and 



contains a cavity called the archenteron; adj., gastrular. 

 gastrulation (gfts trob la' shQn). The development of a gastrula from a blastula. 

 gemmation (jf^m a' shun). Reproduction by budding, 

 gemmule (jeni' ul). A bud of a fresh-water sponge, produced internally and inclosed 



in a cyst, which lives over winter and develops in the spring. 

 gen (jen). G.; producing, causing; gener (jfn' gr), born. 

 gene (jen). That in the chromatin of a germ cell which by interaction with other 



genes and the cj^toplasm determines the production of a character in the indi- 

 vidual developed from the cell; the unit of inheritance, 

 gener (j6n' er). L.; race, kind. 

 genotype (jen' 6 tip). An organism considered with reference to its total genetic 



constitution; adj., genotypic (j6n 6 tip' Ik). 

 geotropism (je 6t' ro piz'm). The response of an organism to the force of gravity; 



adj., geotropic (je 6 trSp' Ik). 

 germ cell. A cell concerned with reproduction; adj., germinal (jur' ml nftl). 

 germ layers. Cell layers formed early in embryogeny from which the definitive 



tissues are developed. 

 germplasm (jurm' plftz'm). The portion of the protoplasm of a germ cell which 



transmits the hereditary characters. 

 gill. An organ for respiration under water. 

 gizzard. A portion of the alimentary canal in annelids and birds the function of 



which is to grind the food. 

 gland. An organ which produces a secretion; adj., glandular (glan' du lar). 

 glochidium (glo kid' I um). The larva of a fresh-water mussel, 

 glomerulus (glo mSr' oo lus). A mass of tissue containing a knot of blood capillaries 



inclosed by the end of a kidney tubule of the mesonephroi and metanephroi of 



vertebrates. 

 glottis (glot' Is). A slitlike opening from the pharynx into the larynx or trachea in 



the higher vertebrates. 

 glycogen (gli'kojen). The form in which carbohydrate food is stored in the liver 



and other tissues; also called animal starch. 

 gnath (nath). G.; jaw. 



gon (gon). G.; seed, referring to reproduction. 

 gonad (gon' Sd). An organ which produces egg cells or sperm cells. 

 Grassi (gras' e), Giovanni B. Italian zoologist; 1854-1925. 

 gregariousness (gre ga' rl us n6s). As used in this text, the tendency of animals of 



different species to gather together. 

 gustatory (gus' ta to rl). Pertaining to the sense of taste. 



Habit. A mode of action, or an act which when first performed has no relation to 

 an action pattern, but in connection with the contiruied repetition of which an 

 action pattern is developed, and which comes to control the animal in the same 

 manner as does an instinct. 



