Appendix 833 



Gastric (gas' trik) (Gr. gaster, stomach), pertaining to the stomach or to 

 digestion. 



Gastrovascular (gas tro -vas' ku lar) (Gr. gaster, stomach; L. vasculum, vessel or 

 circulation) digestive-circulatory cavity as in Hydra. 



Gastrulation (gas troo -la' shun) (Gr. gaster, digestive), the formation of the gas- 

 trula stage in embryonic development by an invagination (infolding) 

 process whereby the future digestive tract will be formed. 



Gel (jel) (L. gelare, to stiffen), state of a colloidal system in which the external 

 phase is more solid than the internal phase (jellylike colloid). 



Gelation (jel -a' shun) (L. gelare, to stiffen), the phenomenon of forming a gel. 



Gemma (gem' a) (L. gemma, bud), small, green, asexual reproductive bodies 

 found in such plants as the Marchantia (Liverwort). 



Gemmule (gem'ul) (L. gemma, bud), asexual reproductive body of several cells 

 found in certain sponges. 



Gene (jen) (Gr. gen, to form), factor (determiner) in a chromosome which influ- 

 ences the development of a hereditary trait. 



Genetics (je -net' iks) (Gr. genesis origin), science of trait transmission from par- 

 ents or other ancestors to offspring. 



Genital (jen' i tal) (L. gignere, to beget), pertaining to reproduction. 



Genotype (jen' o tip) (Gr. genos, race; typos, model), hereditary constitution of 

 an organism or a group of organisms based upon gene content (contrast 

 with Phenotype). 



Genus (je' nus) (Gr. genos, race), somewhat similar organisms having one or more 

 species which are structurally or phylogenetically related. 



Geographic distribution (biogeography), distribution of plants and animals in dif- 

 ferent geographic areas. 



Geotropism ( je -ot' ro pizm) (Gr. ge, earth; trope, turning), reaction of organisms 

 to gravity. 



Germ cell, male or female reproductive cell. 



Germinal continuity (jurm' i nal) (Gr. germen, offspring), the unbroken, con- 

 tinuous stream of germ plasm from one generation to another. 



Germinal variation, variation arising in a germ cell. 



Germ layer, two or three embryonic cellular layers from which future adult tis- 

 sues and organs arise. 



Germ plasm, material basis of inheritance found in germ cells (sex cells) and 

 transmitted by them to the cells of the offspring. 



Germ theory of disease, certain types of diseases are caused by microorganisms. 



Gestation (jes -ta' shun) (L. gestatio, to bear), carrying of young (normally in 

 the uterus) from conception to delivery (birth). 



Gill, filamentous or platelike structure with blood vessels for respiration in water. 



Gill book, specialized, booklike organ of respiration in certain Arachnida. 



Gill slits, paired openings in vertebrates connecting the pharynx with the exterior 

 and permitting the exit of water (same as pharyngeal cleft). 



Gizzard (giz' ard) (Fr. giser, gizzard), muscular grinding organ for digestion. 



Gland (L. glans, nut), a cell or group of cells for secretion. 



Glochidium (glo -kid' i um) (Gr. glochis, arrow point), bivalved larva of mollusks 

 which live parasitically, on a fish for a time. 



