GLOSSARY 381 



Evagination. The folding of a layer of cells outward from an enclosed cavity. 

 Evolution. The gradual or sudden change of animals or plants through successive 



generations. 

 Evolve. To change; to undergo evolution. 



Excretion. The elimination of waste substances. Also a substance excreted. 

 Exhalent. Breathing out; applied to one of the siphons of a clam or mussel. 

 Exophthalmic goiter {cks' of thai' mik). A disease resulting from overactivity of the 



thyroid gland, and having as one of its symptoms the bulging of the ej-es. 

 Exoskeleton. A skeleton on the outside of the body, as in the arthropods. 

 Extensor. A muscle whose contraction straightens a joint. 

 External respiration. The passage of oxygen from the surrounding air or water to 



the blood. 



Fi (ef unin'). An individual or generation of individuals resulting from the crossing 



of two unlike parents. An abbreviation of the words first filial. 

 Fi {ef too'). An individual or generation of individuals resulting from the mating of 



two Fi individuals as parents. An abbreviation of the words second filial. 

 Family. A taxonomic group of higher rank than the genus but below the order. 

 Fat. A compound of glycerol and one or more fatty acids. 

 Fatty acid. An organic acid entering into the composition of fats. 

 Fauna. Collectively, the animals of a given region or of a given period of time. 

 Femur. The single bone of the thigh in vertebrates above the fishes. 

 Feral. Plscaped from domestication. Also, sometimes, wild. 

 Fertilization. The union of an egg with a spermatozoon, a process requisite, in the 



higher animals, to the development of the egg. 

 Fetus (/(' tus). The embryo of a mammal while still in the uterus. 

 Fibril. One of the longitudinal contractile threads of a voluntary muscle cell. 

 Fibrin. A substance in blood which forms much of the clot on escape from the 



vessels. 

 Fibrinogen (fi. brin' ojen). A soluble protein carried in blood plasma, from which 



the insoluble fibrin of a clot is formed. 

 Fibula (fib' u la). The outer one of two bones in the lower leg of vertebrates except 



the fishes. 

 Fission. The division of an organism into two approximately equal parts ; or, simply, 



division. 

 Flagellate iflaj' el late). Possessing flagella. As a noun, a flagellate protozoon. 

 Flagellum [pi., flagella). A long whiplike motile projection from a cell. 

 Flame cell. A cell having a hollow interior in which a bunch of vibratile cilia are 



located, forming part of a protonephridium. 

 Flexor. A muscle whose contraction bends a joint. 

 Fluke. Any one of several species of trematode worms. 

 Follicle. A layer of cells surrounding some object, as an ovum in an ovary. 

 Foot. The basal muscular part of a clam or snail, variously modified in many other 



mollusks. Also the terminal part of a leg, the base of Hydra, etc. 

 Foraminal aperture (/o ram' i nal). In a sponge gemmule, the opening in the shell 



through which the young sponge escapes when it begins to develop. 

 Formation. The rocks belonging to one of the minor divisions (lower than epoch) 



of geological time. 

 Fossil. The remains, or other indication, of a prehistoric animal or plant. 

 Fructose. A simple sugar (monosaccharide) found in fruit juices, and one of the 



products (with glucose) obtained by breaking down sucrose (cane sugar); same 



as levulose. 



