GLOSSARY 437 



EUSTACHIAN TUBE. Passage connecting the Vertebrate middle ear 

 with the pharynx. Remnant of the most anterior gill slit, rep- 

 resented in present-day Sharks by the 'blow-hole,' or spiracle. 



EUTHENICS. The system of improving the human race by good 

 environment. See Eugenics. 



EUTHERIA. The highest of the three subclasses of Mammals, 

 including all the familiar forms. See Appendix I, Classification. 



EVOLUTION, ORGANIC. The accepted theory that present-day 

 organisms are the result of descent with modification, or change, 

 from those of the past. The word ' modification' is not used in 

 the technical sense employed in genetics. See Modifications. 



EXCRETION. The elimination of waste products of metabolism. 

 The waste products themselves. See Secretion. 



EXOPODITE. The outer of the two distal parts of the typical, bira- 

 mous, Crustacean appendage. See Protopodite and Endopodite. 



EXOSKELETON. A non-living external skeleton chiefly for protec- 

 tion. The characteristic skeleton of Invertebrates, e.g., Cray- 

 fish. 



EXTERNAL RECEPTORS. Sense organs upon the surface of the body. 

 See Internal Receptors. 



EXTRACTED DOMINANT. A homozygous individual, exhibiting 

 the dominant character, derived from heterozygous (hybrid) 

 parents. 



EXTRACTED RECESSIVE. An individual exhibiting the recessive 

 character, necessarily homozygous, derived from heterozygous 

 (hybrid) parents. 



FAMILY. In classification, a main subdivision of an order. See 

 Genus. 



FATS. One of the chief groups of foodstuffs. Organic salts con- 

 sisting of the glycerol radical (C 3 H & ), the basic part, combined 

 with a fatty acid. E.g., mutton tallow is chiefly the fat Stearin 

 (C 5 7Hno0 6 ) = Glycerin plus Stearic acid. 



FERMENTATION. The transformation of organic substances chiefly 

 through the activity of ferments, or enzymes, derived from 

 living organisms. See Putrefaction. 



FERTILIZATION. The union of male and female gametes, especially 



