GLOSSARY 



673 



genesis, birth ) . The process of development 

 of gametes. 



Gau'gli-on (Gr. ganglion, enlargement). A 

 group or mass of nerve cell bodies, usually 

 located outside the central nervous system 

 in vertebrates; in invertebrates, ganglia oc- 

 cur within the central nervous system. 



Gas'tric (Gr. gaster, belly). Pertaining to the 

 stomach, as the gastric glands. 



Gas'troc-ne"mi-us (Gr. gaster, belly; kneme, 

 tibia ) . The large muscle on the posterior 

 side of the lower leg of a vertebrate. 



Gas'tro-vas^'cu-lar (Gr. gaster, belly; L. vas- 

 culum, vessel) . Serving the functions of both 

 digestion and circulation. 



Gas'iru-la (Gr. gaster, belly). A stage in de- 

 velopment in which the embr)'o usually con- 

 sists of two germ layers (ectoderm and en- 

 doderm) with a cavity surrounded by en- 

 doderm. 



Gas'tru-la"tion (Gr. gaster, belly). Process by 

 which a gastrula is formed; the invagination 

 of the blastula. 



Gene (Gr. genesthai, to be produced). A unit 

 of hereditv which is transmitted in the 

 chromosome and which by interaction with 

 the internal and external environment con- 

 trols the development of a trait (character); 

 the hereditary determiners. 



Ge-net'ics (Gr. gignesthai, to be born). See 

 Heredity. 



Gen'i-tal (L. gignere, to beget). Pertaining to 

 the reproductive organs of either sex. 



Gen'o-type (Gr. genesthai, to be produced; 

 typos, impression). The entire genetic make- 

 up of an individual which shows how it will 

 breed. It tells the kind of genes an individ- 

 ual has. Compare with Phenotype. 



Ge'nus (L. genere, to beget). The taxonomic 

 subdivision of a family. A genus is usually 

 composed of several species. Genus names 

 are Latinized, capitalized; and, when 

 printed, italicized. 



Ge-ot'ro-pism (Gr. ge, earth; repein, to turn). 

 The response in behavior of an organism 

 to gravity. 



Germ cell (L. germen, germ. L. cella, com- 

 partment). Gametes, or cells which give rise 

 to gametes. 



Germ lay'er (L. germen, germ). One of the 

 primary cell layers in an embryo; ectoderm, 

 endoderm, or mesoderm. There are no 



permanent or clear-cut distinctions, as shown 

 by transplantation experiments, yet in the 

 mammal development each tends to pro- 

 duce separate parts. 



Germ plasm (L. germen, germ. Gr. plasma, 

 something molded). The material basis of 

 heredity. Weismann's term for the heredi- 

 tary substance in the germ cells. 



Ges-ta'tion (L. gerere, to carry). The period 

 between fertilization and birth of a mam- 

 mal. 



Gill (Gr. cheilos, lip). A type of respiratory or- 

 gan for aquatic organisms. 



Gill arches (Gr. cheilos, lip. L. arcus, bow). 

 The walls adjacent to the gill slits; walls 

 bearing the gills. 



Gill slit (pharyngeal cleft) (Gr. cheilos, lip. 

 A.S. slitan). A series of paired openings in 

 the wall of the phar\'nx and body of chor- 

 dates. 



Giz'zard (Fr. giser, gizzard). A muscular part 

 of the digestive tract, as in earthworms, in- 

 sects, and birds, used for grinding ingested 

 food. 



Gland (L. glans, acorn). One or many asso- 

 ciated cells that secrete or excrete one or 

 more special substances. 



Glo-mer'u-lus (L. glomare, to make a ball). A 

 small coiled mass of capillaries contained in 

 the Bowman's capsule of the vertebrate kid- 

 ney. 



Glot'tis (Gr. glotta, tongue). The opening 

 from the phar\nx into the larynx of a verte- 

 brate with lungs. 



Gly'co-gen (Gr. glykus, sweet; gen, produc- 

 ing). A form of carbohydrate (polysac- 

 charide) food material stored in the liver, 

 muscles, and some other tissues; an "animal 

 starch." 



Gob'let cell (L. cuppa, cup. L. cella, compart- 

 ment). A modified epithelial cell which se- 

 cretes mucus. 



Go'nad (Gr. gonos, reproduction). Reproduc- 

 tive organ, either ovary, testis, or ovotestis, 

 in which gametes are produced. 



Go-nan'gi-um (Gr. gone, seed; angeion, ves- 

 sel ) . The reproducti\e individual of a hy- 

 droid colony. 



Gon'o-the"ca (Gr. gone, seed; theke, cup). 

 The firm external covering of a gonangium. 



Grc-gar'i-ous (L. gregarius, from grex, herd). 

 Living in company, as in flocks and herds. 



