has an insufficient supply of oxygen; occur- 

 ring mostly at high altitudes. 



antenna (an-ten'na) : one of a pair of projecting 

 sense organs on the head of insects, crusta- 

 ceans, etc. 



anterior (an-teer'i-er) : applied to the front or 

 head end of an animal. 



anther: the pollen case found on the top part of 

 the stamen in a flower. 



anthropologist (an-throw-pol'oh-jist) : one who 

 studies the science that treats of the origin, 

 classification, and culture of man. 



antibiotics (an'ti-hy-ot'ticks) : substances pro- 

 duced by living organisms and used in medi- 

 cine to kill or hinder growth of disease- 

 producing organisms. Example is penicil- 

 lin. 



antibody (an'ti-bod'y) : any of the various sub- 

 stances which are formed by the animal body 

 and which counteract foreign organisms or 

 their products. 



antiseptic (an'ti-sep'tic) : substance which pre- 

 vents the action of germs and hinders their 

 increase in numbers. 



antitoxin (an'ti-tox'in) : substance formed in the 

 body of an animal which counteracts a par- 

 ticular toxin (poison) made by an organism. 



aorta (ay-or'ta) : single large artery in verte- 

 brates which leads the blood out of the heart 

 to be distributed to parts other than the 

 lungs. 



aphids (ay'fids) : small insects living on plants 

 and sucking their juices. 



appendage (ap-pend'aj) : any part of the body of 

 an animal arising from the main trunk, such 

 as a leg. 



appendix: in man and some other mammals a 

 narrow outgrowth from the blind sac at the 

 beginning of the colon. 



arachnids (a-rack'nids) : members of one of the 

 five large classes of the arthropod phylum, 

 such as spiders. 



archaeornis (are-key-or'nis) : extinct birdlike ani- 

 mal which had teeth and a long tail with 

 vertebrae. 



artery: blood vessel that carries blood away from 

 the heart to capillaries. 



arthropods (are'thro-pods) : members of a large 

 phylum of invertebrates which have a seg- 

 mented body, jointed legs, and a firm cover- 

 ing (exoskeleton). 



artifact (are'te-fact) : any article made by man 

 for his use, especially products made by pre- 

 historic man. 



ascorbic (ay-skor'bic) acid: vitamin C; prevents 

 scurvy. 



aseptic (ay-sep'lic) : free from living microorgan- 

 isms which might cause disease, fermentation, 

 or decay. 



asexual (ay-sek'shoo-al) reproduction: forming of 

 a new individual williout llic uniting of two 

 cells. 



assimilation (as-sim'il-ay'shun) : changing food 

 substances to protoplasm in the cell. 



auricles (or'i-k'ls) : chambers in the vertebrate 

 heart which receive blood from veins and 

 send it to the ventricles. 



autonomic (au-toh-nom'ic) nervous system: sys- 

 tem of nerves and ganglia which works closely 

 with the central nervous system and controls 

 the behavior of some of the internal organs. 



auxin (awk'sin) : class of substances which in 

 very small amounts regulate the growth of 

 particular parts of plants; sometimes called 

 growth hormones. 



axon (ak'son) : part of a neuron; projection from 

 the cell body carrying impulses out of the 

 cell. 



bacillus (ba-sill'us) : rod-shaped bacterium. 



bacteria, pi. of bacterium: microscopic fungi, very 

 simple in structure, of many species; most 

 are useful, some very harmful. 



bacteriology (back-teer'iy-ol'o-jee) : study of bac- 

 teria and their effects. 



bacteriophage (back-teer'iy-o-faj) : a filterable, 

 ultramicroscopic agent which breaks up cer- 

 tain bacteria. 



balanced aquarium: aquarium in which under 

 proper conditions of light and temperature 

 the plant and animal organisms produce sub- 

 stances necessary to each other in quantities 

 that enable both kinds to live. 



bark: tough, often hard, external covering of 

 woody stems. 



behavior: the sum total of the responses of an or- 

 ganism to its environment. 



beriberi (ber'ree-ber'ree) : deficiency disease 

 caused by an insufficient intake of vitamin Bi 

 (thiamin). 



bicuspids (bye-kuss'pids) : teeth with two points, 

 lying between the canines and molars in 

 mammals; also known as premolars. 



biennial (bye-en'i-al) : plant that lives for two 

 growing seasons, bearing flowers and fruits 

 the second year. 



bilateral symmetry (bye-lat'e-rel sim'e-tree) : ar- 

 rangement of the parts in an animal in such 

 a way that the right and left sides are simi- 

 lar. 



bile: bitter greenish liquid secreted by the liver; 

 stored in the gall bladder. 



binary fission (bye'na-ree fish'un) : division in half 

 of a one-celled organism in asexual reproduc- 

 tion. 



biology: study of living things. 



birds: members of a class of vertebrates distin- 

 guished by a covering of feathers. 



blade: broad part of a leaf as distinguished from 

 llie petiole (stalk). 



blastula (blast'you-la) : an early stage (a hollow 

 ball of cells) in the development of the em- 

 bryo of many kinds of majiy-celled animals. 



bleeders: persons who have hemophilia. 



blending inheritance: inheritance in which there 



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