212 ECOLOGY AND LIFE HISTORY OF THE COMMON FROG 



Correlation Coefhcient, Partial. A correlation coefficient so computed 



that the effect of other variables has been ehminated. 

 Correlation Coefhcient, Rectilinear. A correlation coefficient computed 



on the assumption that the relation between the variables can be expressed 



as a straight line. Often abbreviated to "linear correlation coefficient." 

 Covariance. a measure of the variabihty in two sets of numbers, occurring 



in pairs. The mean of the products of the deviations from the respective 



means. 

 Crustacea. A family of animals including crabs, but in this context, "the 



water fleas" of fresh water. 

 Cysts. Resting stages. 

 Degrees of Freedom. The numbers of classes in a statistical classification that 



can be independently varied. 

 Density Dependent Factors. Factors that affect animal populations so that 



the effects are greater when the population of animals is dense than when it 



is sparse. 

 Diatoms. Algae with a skeleton of siHca. 



DiHYDROL. A polymer, consisting of two molecules of water, (H20)2. 

 Distribution Curve. The curve obtained by plotting the frequency of an 



event against its magnitude. 

 Ecology. The study of animals in their natural homes. 

 Endocrinology. The study of the glands of internal secretion and of the 



hormones they secrete. 

 Enzyme. An organic substance accelerating a biochemical reaction. In practice 



often essential for the reaction to occur at all. 

 Epizootic. Disease affecting numbers of animals. Corresponds to "epidemic" 



in humans. 

 Fibrin. The thread-like insoluble protein forming the structure part of a blood- 

 clot. 

 Fibrinogen. A soluble protein in blood, forming fibrin when acted upon by 



thrombin. 

 Fluke. Trematode. 

 Food Chain. The chain of events such as this : Plant eaten by Animal A, 



Animal A eaten by Animal B, Animal B eaten by Animal C. . . . 

 Gel. Jelly. May become a sol. See "Sol." 



Geotaxis. Movement against gravity (negative), or with gravity (positive). 

 Glottis. The opening of the wind-pipe into the pharynx. 

 Gonads. The organs producing eggs in the female or sperm in the male. 

 Haematology. The study of the blood. 

 Hibernacula. The winter quarters of animals that hibernate. 

 HoMOiOTHERMAL Animal. An animal that can regulate its internal temp- 

 erature, within limits, independently of the external temperature. Birds and 



