854 Appendix 



Q 



Quadruped (quard' ru ped) (L. quattuor, four; pes, feet), four-footed animal. 

 Quard' ruplet, one of four offspring born at the same time. 



Quaternary (qua' ter na ri), the last of the great fossil-bearing rocks (Pleis- 

 tocene). 

 Queen, the reproductive female in colonies of social insects. 



R 



Radial canal (L. radius, ray), canal radiating from a center as in starfish. 



Radial synmietry, arrangement of similar parts around a central point like the 

 spokes of a wheel. 



Radicle (rad' i cl) (Gr. radix, root), primary root of seedlings. 



Radioactivity, a condition in which there is a partial disintegration of atoms, with 

 the shooting out from the atomic nucleus of alpha particles, electrons, 

 x-rays, etc. 



Radioulna, fused radius and ulna bones of frog forearm. 



Radius (ra' di us) (L. radius, rotate), rotating bone of forearm. 



Radula (rad' u la) (L. radere, to scrape), scraping organ for mastication in 

 certain Mollusca as snails. 



Recapitulation theory (re ka pit u -la' shun) (Gr. re, again; caput, head), the life 

 history of an individual repeats (recapitulates) in an abbreviated man- 

 ner the ancestral history of that race as a whole {see Biogenetic theory). 



Receptor (re-sep'ter) (L. receptor, receiver), receiving sensory cell or organ. 



Recessive characters, those traits which are not expressed, even though their 

 genes are present together with the gene for the opposite, allelomorphic 

 dominant. 



Rectum (rek' tum) (L. rectus, straight), posterior part of intestine. 



Red blood corpuscle, oxygen-carrying cell. 



Redia (re'dia) (after Italian naturalist, Rcdi), the second type of larva found 

 in life cycle of flukes. 



Reduction division, the division of chromosomes of maturing gametes in which 

 the normal, diploid, somatic number of chromosomes is reduced to the 

 haploid, single number. 



Reflex action (L. re, back; fiectere, to return), automatic, involuntary response 

 of nervous and motor mechanisms to stimuli. 



Refraction (re -frakt' shun) (L. re, back; frango, break), deflection of light waves 

 when passing obliquely from one medium to another with different re- 

 fractive indices. 



Regeneration (re gen er -a' shun) (L. re, again; generare, to beget), ability to 

 replace a lost part or develop a new individual from a lost part. 



Renal (re' nal) (L. renes, kidney), pertaining to kidney. 



Renal portal system (L. renes, kidney; porta, gate), blood vessels (veins) carry- 

 ing impure blood from the posterior part of the body to the kidneys. 

 Oxygenated blood is carried to the kidneys by renal arteries. Fishes, 

 amphibia, and reptiles have this double blood supply for the kidneys, while 

 this system is vestigial in birds and absent in mammals. 



Rennin (ren' nin) (A.S. rennan, run), milk-coagulating enzyme. 



