400 PRINCIPLES OF ANIMAL BIOLOGY^ 



Range (rninj). The area occupied by a species or larger taxonomic group of animals 

 or plants. 



Ray, John (ray). English naturalist, 1627-1705. 



Reaction (re ak' shun). Any response of an animal to a stimulus. 



Recapitulation theory (re' ka pit' u la' shun). See biogenetic law. 



Receptacula seminis (res' ep taV u la sem' i nis). Chambers in which one animal 

 stores sperms received from another. 



Recessive (re ses' siv). Not being produced when the gene for a contrasted domniant 

 character is also present ; said of inherited characters that are concealed in hetero- 

 zygotes. 



Rectum (rek' turn). The terminal portion of the large intestine in the higher verte- 

 brates. In vertebrates with a cloaca, the term is sometimes applied to the part of 

 the large intestine anterior to the cloaca. 



Redi, Francesco (ra' dee). An Italian naturalist and poet, 1626-1698. 



Redia (re' di a). One of the individuals in the life cycle of the liver fluke Fasciola 

 (and similar forms) which are parthenogenetically produced by the sporocyst. 



Reduction (re duk' shun). Cell division in which chromosomes are not split, but merely 

 separated from one another after having previously come together in pairs, as 

 occurs in one of the two maturation divisions in bisexual reproduction. 



Reflex (re' fleks). Same as reflex action. 



Reflex action (re' fleks ak' shun). An action performed as a result of an impulse 

 which passes over a reflex arc. It is involuntary and is often performed without 

 the consciousness of the organism. 



Reflex arc (re' fleks ark'). A group of two or more neurons, one of them sensory, 

 another motor, so connected as to be able to transmit impulses resulting in reflex 

 actions. 



Regeneration (rejen' er a' shun). The production of lost parts by organisms. 



Remak, Robert (re niahk'). A German neurologist, 1815-1865. 



Rennin, (ren' nin). An enzyme produced by the gastric glands and having the 

 property of coagulating milk. 



Reproduction (re' pro duk' shun) . The formation of new individuals among organ- 

 isms. 



Reptilia (rep til' i a). A class of vertebrate animals including the snakes, lizards, croco- 

 diles, turtles, and some others. For definition see Chapter XII. 



Respiration (res' pi ra' shun). The absorption of oxygen by protoplasm. The term 

 is sometimes loosely applied also to the forcing of air to and from respiratory organs 

 like the lungs, a process more properly called breathing. 



Reticular (re tik' u ler). Of the nature of a network; said of certain forms of proto- 

 plasm or cell structure. 



Reticulum (re tik' u lum). A network. 



Retina (ret' i 7ia). The sensitive inner layer of the eye of vertebrates and some other 

 animals. 



Retractile (re trak' til). Capable of being withdrawn. 



Rhabdocoele (rab' do seel). A flatworm (Platyhelminthes) of the order Rhabdocoelida. 



Rhinozoa (ri' no zo' a). A group of animals (literally, nose animals) in Ok en's early 

 classification. It comprised the reptiles. 



Rhizopoda (rizop'oda). A class of Protozoa having a form that is changeable 

 through the production of pseudopodia; example, Aiuceba. 



