214 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



Phanerogams. The flowering plants. 



Pharynx. The part of the ahmentary canal between the mouth and the 



glottis. 

 Phenology. The study of the dates of natural events in the Hves of animals and 



plants. 

 Phototaxis. Movement towards the Hght (positive), or away from it 



(negative). 

 Plankton. Animals or plants that float near the surface of the water. 

 Plasma. The Hquid part of blood, in which the red cells float. 

 PoiKiLOTHERMAL Animal. An animal whose body is at or near the temperature 



of its environment, because it has no power of regulating its internal 



temperature. 

 Polymer. A substance consisting of two or more simple molecules. 

 Precipitation. Rain, snow or hail. 

 Predators. Animals that prey on other animals. 

 Protein. The main nitrogenous constituent of Hving matter. 

 PoLYSTOME. An Anglicized version of the name of the genus of trematodes, 



Polystoma. 

 Prothrombin. One of the substances in blood plasma that plays a part in the 



coagulation of the blood. 

 Protozoa. Unicellular animals. 



Regression Curve. Curve expressing the relation between two variables. 

 RjBGRESsiON Curve, Net. A regression curve from which the effect of other 



variables has been eliminated by statistical means. 

 RjBLEASER. In an animal, the signals that "release" sequences of behaviour. 

 SiGNincANT. In this book, always used in the statistical sense, meaning : "Not 



due to chance." Never used here as a synonym of "important." 

 Standard Deviation. A measure of variabiUty. The square root of the 



variance. 

 Sol. a solution of a substance of high molecular weight, or of aggregates of 



simpler substances with a high total molecular weight. May become a gel. 



See ("gel"). 

 Species. The smallest clearly distinguishable unit in the classification of animals 



or plants. 

 Spiracle. The tubular exit from the atrium. 

 Symphysis Pubis. The junction between the pubic bones. 

 Thrombin. The enzyme, formed in blood, that reacts with fibrinogen to form 



fibrin. 

 Thromboplastin. A substance formed in blood when it clots. 

 Trematodes. Parasitic flat worms. 



Trihydrol. a polymer, consisting of three molecules of water, (H20)3. 

 Tropism. a turning reaction by an animal. 



