382 PRINCIPLES OF ANIMAL BIOLOGY 



Funiculus {fu nik' u lus). A muscular strand which draws the body of a br^yozoan 



into a U shape. 

 Furcula (fur' ku la). The wishbone of a bird, consisting of the fused clavicles of the 



two sides. 



Galactose (ga lak' lose). A simple sugar (monosaccharide) obtainable by breaking 

 down lactose, or lipids of the brain. 



Galen. Famous Greek physician and anatomist, born about a.d. 130. His writings 

 were long the highest authority in medical science. 



Gall bladder. A pouch in which the bile secreted by the liver is stored. 



Gamete (gajn' eet). A germ cell, or other cell which fuses with a second cell in repro- 

 duction. 



Gametogenesis (ga me' to jen' e sis). The ripening of germ cells. 



Ganglion (gang' gli on) (pi., ganglia). A mass of nerve cell bodies, usually forming 

 a thickening in the course of a nerve. 



Gastric. Pertaining to the stomach. 



Gastrocnemius (gas' trok ne' mi us). A large muscle in the calf of the leg in verte- 

 brate animals. 



Gastropoda [gas Irop' o da). A class of Mollusca including snails and slugs, mollusks 

 whose bilateral symmetry is often obscured by a coiled bodj' and shell. 



Gastrotheca. A genus of frogs. 



Gastrovascular. Serving the functions of digestion and circulation. 



Gastrovascular cavity. See coelenteron. 



Gastrula {gas' tru la). An early developmental stage, formed from a blastula, com- 

 monly by the invagination of the vegetative pole of the latter. The gastrula 

 consists of two layers of cells (ectoderm and endoderm) surrounding a cavity 

 which communicates with the exterior. 



Gastrulation. The formation of a two-layered embryo from a blastula, by invagina- 

 tion of the vegetative pole, by delamination, or otherwise. 



Gemmule. A group of cells forming a reproductive body in fresh-water sponges. 



Gene. Something in a germ cell or other cell which is responsible for a hereditary 

 characteristic. 



Generic (je ner' ic). Pertaining to a genus. 



Genetics. The science of heredity, variation, sex determination, and related phe- 

 nomena. 



Genital. Concerned with reproduction. 



Genus (je' nus) (pL, genera, jen' e ra). A group of species having so many structural 

 features alike that they must be regarded as having sprung from common ances- 

 try; a group of lower rank than the family. 



Geoflfroy Saint-Hilaire, Etienne (zho frwa' sa^ ie lair'). French naturalist, 1772- 

 1844. 



Gephyrea (je fi' re a). A group of wormlike aninuils of doubtful rank and relation- 

 ships. Thej^ have sometimes been referred to the Annelida. 



Germ cell. A cell capable of reproduction, or of sharing in reproduction, as con- 

 trasted with the somatic or body cells which are sterile; or, more strictly, a repro- 

 ductive cell that has undergone, or will undergo, or whose cell descendants will 

 . undergo, oogenesis or s{)orniatogenesis before partici])ating in reproduction. 



Germ layers. The embryonic layers, ectoderm, endoderm, and mesoderm; so called 

 because, in a sense, each one contains the "germ" of certain adult structures. 



Gill. A structure having a surface enlarged usually by branching or folding, which 

 serves a respiratory fimction. 



Gill bar. The tissue between two gill clefts. 



