quarantine (kwar'iin-teen) : prevention by those 

 in aulixority of free movement of people, 

 other living things, or goods in order to stop 

 the spread of disease. 



race: in the classification of man a subdivision of 

 a stock composed of people who tend to have 

 certain inborn physical characters in com- 

 mon, such as Nordic and Hindu races. 



radial symmetry (ray'dee-el sim'e-tree) : arrange- 

 ment of parts in an animal in such a way that 

 the parts radiate from a central point, as the 

 arms of a starfish. 



receptors: sense organs which keep an animal in 

 touch with the environment, such as the eyes, 

 ears, taste buds, etc. 



recessive: in genetics, that character of a pair of 

 contrasting characters that does not show in 

 the hybrid offspring, as shortness in pea 

 plants; applied also to the gene. 



reduction division: nuclear division in which the 

 number of chromosomes is reduced to half: 

 reduction division in higher plants and ani- 

 mals occurs just before or at the time sperms 

 and eggs develop. 



reflex act: in an animal a direct response to a 

 stimulus which is immediate, which is inborn 

 and therefore predictable, and which may or 

 may not be accompanied by consciousness of 

 the act. 



reflex arc: path of a nerve impulse from a recep- 

 tor, along an afferent neuron, through the 

 brain or cord, and out along an efferent neu- 

 ron to the cells that respond. 



regeneration (ree-jen-er-ay'shun) : growing back 

 of a part of an organism or a part of a cell 

 which has been lost by injury, as the arm 

 of a starfish, healing tissues, or the axon of 

 a nerve cell. 



reiinin: enzyme found in our gastric juice; curdles 

 milk. 



reproduction: process by which living things make 

 more of their own kind. 



reptiles: members of a class of vertebrates with a 

 covering of dry scales and breathing by 

 means of lungs, such as snakes, lizards, tur- 

 tles, etc. 



respiration: in animals the process by which oxy- 

 gen is taken into the body and used in oxida- 

 tion, together with the release of the products 

 of oxidation from the body. Cellular respira- 

 tion: whole process in individual cells in 

 animals. In plants respiration is the oxida- 

 tion of foods in the cell. 



response: behavior in living things brought about 

 by a stimulus. 



retina (ret'i-na) : innermost layer of the eyeball 

 in vertebrates, containing the cells sensitive 

 to light. 



Rh factor (R-H factor) : substance in the blood 

 of most people; persons who lack it are said 

 to be RH negative. (Discovered in the Rhesus 

 monkey; hence its name.) 



riboflavin (rye-bo-flay'vin) : vitamin in the B com- 

 plex group; B2, formerly called vitamin G. 



rickets: condition in which the bones fail to de- 

 velop properly, remaining soft; causpd by de- 

 ficiency of vitamin D or calcium or both. 



rodents: members of the order of gnawing mam- 

 mals with strong incisors, such as rats and 

 beavers. 



root hair: microscopic outgrowth from an epider- 

 mal cell of a root; absorbs water and min- 

 erals. 



runner: slender stem growing along the ground, 

 taking root at intervals, and producing new 

 plants at such points, as in the strawberry. 



salivary (sal'i-very) gland: one of three pairs of 

 glands which empty their secretions into the 

 mouth. 



sanctuary (sank'chew-e-ree) : area set aside, usu- 

 ally by the government, in which wildlife is 

 protected; refuge. 



saprophyte (sap'row-fite) : plant that lives and 

 feeds on dead organisms or dead organic 

 matter. 



science: organized facts and "laws" about the 

 world and living things; also the method by 

 which men reach understandings about the 

 world and living things. 



scion (sy'on) : in grafting, the twig or bud at- 

 tached to the growing plant. 



sclera or sclerotic coat: dense fibrous membrane, 

 forming with the cornea the outermost coat 

 of the eyeball. 



scurvy: deficiency disease caused by insufiBcient 

 intake of vitamin C. 



secondary sex characters: bodily characteristics, 

 other than the sex organs themselves, which 

 in many higher animals distinguish the male 

 from the female, such as bright plumage in 

 male birds. 



secretin (see-cree'tin) : hormone produced by the 

 small intestine which stimulates the pan- 

 creas to secrete its digestive juice. 



secretion (see-cree'shun) : producing and giving 

 off useful substances by cells or groups of 

 cells in plants and animals; cells or groups 

 of cells specially fitted for this are called 

 glands. 



sedimentary rock: rock formed from sand or mud 

 laid down as a sediment in water and finally 

 compressed into rock. 



seed: ripened ovule containing an embryo plant. 



seedling: young plant from the time it emerges 

 from the seed until it is entirely dependent 

 on food made by itself. 



segment: one of the rings that compose the body 

 of annelids, most arthropods, and chordates. 



segregation, law of: law stating that the two 

 members of a pair of genes separate in re- 

 duction division without having changed one 

 another. As stated by Mendel: in the cross- 

 ing of hybrids the recessive character shows 

 up in the offspring; the ratio in the offspring 



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