676 Glossary 



Flexion — a type of movement that involves the bending of a joint. 



Fontanel — a space between the bones of the skull of a fetus or very young 



animal that is covered by a membrane. Here tiie blood may be seen 



to pulsate, suggesting a fountain. 

 Foramen — a small opening. 

 Fossa — a depression. 



Fovea — the place on the retina of the eye where vision is most acute. 

 Frenulum — a fold of tissue that binds the underside of the tongue. 

 Frontal plane — plane parallel to dorsal (or ventral) surface. 



Gamete — a matured sex cell; egg or sperm. 



Gametogenesis — the process by which gametes are formed. 



Ganglion — a mass of nerve cell bodies located outside the central nervous system. 



Gastrovascular — functioning both for digestion and circulation; a type of cavity 



found particularly among the coelenterates, ctenophores, and flatworms. 

 Gastrula — an embryonic stage. 



Gene — an hereditary factor located on the chromosome. 

 Genotype — the genetic composition of an organism. 

 Genus — a category of classification more inclusive than the species but less than 



the family. 

 Gill — a respiratory structure. 



Gizzard — a portion of the digestive tract where food is ground. 

 Gland — a secreting structure. 



Glottis — the opening of the respiratory tract found on the floor of the pharynx. 

 Glycogen — carbohydrate related to starch ; found in the liver of most animals. 

 Gonad — a general name for either the testis or ovary. 



H 



Haploid — having half the number of chromosomes present in the body cells ; the 



number characteristic of the egg and sperm. 

 Haversian canal — passageway in bone. 

 Heart — the pumping organ of the circulatory system. 

 Hemoglobin — the respiratory pigment of the red blood cells. 

 Hemophilia — a condition, usually hereditary, in which the blood does not clot 



properly. 

 Herbivorous — having a diet consisting chiefly of plant material. 

 Hermaphroditic — having both male and female organs in the same individual. 

 Heterodont — having the teeth differentiated into various types. 

 Heterogametes — gametes that differ in size, motility, or appearance. 

 Heterozygous — having both genes different for the same character. 

 Holophytic — obtaining nutrition like a plant, that is, manufacturing of food. 

 Holozoic — obtaining nutrition like an animal, that is, feeding on other organisms. 

 Homeostasis — the maintaining of a constant state (with reference to the internal 



medium). 

 Homodont — having teeth all alike. 



