GLOSSARY 



EXPERIMENTAL EMBRYOLOGY. The study of development by altering any one of the 

 conditions affecting its course, such as the external environment. 



EXTERNAL RESPIRATORY EXCHANGE (sometimes EXTERNAL RESPIRATION). See GAS 

 EXCHANGE. 



EXTRA-. Combining form, meaning "outside." 



f , GENERATION. See FIRST FILIAL GENERATION. 

 F_, GENERATION. See SECOND FILIAL GENERATION. 



FACT. A real state of things as distinguished from a belief. 



FACTORS. SV*' GENES. 



FACULTATIVE. Refers to organisms capable of a variety of different processes relating 

 to a common function; for example, some bees, wasps, and other hymenopterans 

 are capable of developing either with or without fertilization of the eggs, and 

 this is spoken of as a case of facultative parthenogenesis. C^J. OBLIGATE. 



FALSE COELOM. See PSEUDOCOEL. 



FAMILY. A subdivision of an order; a group of next higher rank than a genus. 



FATTY ACIDS. A group of organic acids formed by oxidation of alcohols. 



FAULT. Geological term referring to discontinuities in strata of rock, resulting from 

 breakage of the layers after they have buckled under lateral stresses. 



FAUNA. The total of the animal life of a given region or period of time. 



FEMALE GAMETE. .SV^ OVUM. 



FERTILIZATION. The union of two gametes to form a single cell, the zygote; a com- 

 plex process consisting of an initial activation of the ovum, followed by 

 amphimixis. See SYNGAMY; Cf. CONJUGATION. 



FIN. An extension from the body of an aquatic animal, used in locomotion. 



FIRST FILIAL GENERATION. The individuals arising directly from a given mating; 

 the f , generation. See SECOND FILIAL GENERATION. 



FISSION. The division of an organism into two or more parts, each of which usually 

 develops into a new individual; a method of asexual reproduction. 



FLAGELLATE. Having one or more flagella. 



FLAGELLUM {pi. FLAGELLA). A long, whip-like extension from the free surface of a 

 cell, capable of vibration; the locomotor organelle of flagellate protozoans and 

 of most metazoan spermatozoa. CJ. CILIA. 



FLUCTUATION. A modification of a character that is conditioned by some change in 

 the environment during development; a non-heritable variation. CJ. MUTATION. 



FOLLICLE. A cellular sac or envelope. 



FOOD. The material necessary for normal metabolism, that is, for cellular main- 

 tenance and growth and the synthesis of secretions. The source of energy for 

 holozoic organisms. 



FOOD CHAIN. A series of organisms in a community dependent on each other for 

 food supplies; each "link" in the chain feeds upon the organism just below it 

 and in turn serves as food for the one just above it. Different food chains in a 

 community interact to form what are spoken of as "food webs." 



FOSSIL. Anything of organic origin which was buried beneath the surface of the 

 earth by natural causes in prehistoric times. 



FRATERNAL TWINS. Two individuals, not necessarily of the same sex, that arise 

 simultaneously from two zygotes in an animal which usually produces only one 

 young at a time. CJ. IDENTICAL TWINS. 



FREE-LIVING. Not sessile or parasitic; capable of actively obtaining its own food. 



FUNGUS {pi. FUNGI; adj. FUNGOUS). A colorless plant of relatively simple organi- 

 zation. 



GAMETE. A differentiated germ cell, usually ovum or spermatozoon. Cf. SOMATIC 

 CELL. 



665 



