INTRODUCTION TO CYCLES 3 



to determine, control, or affect them. However, before 

 proceeding further, it is necessary to make two defini- 

 tions. The first refers to the term 'breeding season', 

 which is so variously used throughout the literature. 

 Here it is employed in a restricted sense to indicate that 

 period of the year when mating behaviour is evident, 

 and when copulation results in fertilization. It is not 

 used to indicate seasons of incubation, of pregnancy, or 

 of lactation. 



Secondly, in view of the looseness with which these 

 terms are commonly used, it is necessary to state that 

 the seasons of the year are here referred to in a precise 

 sense. 8 In northern temperate regions, spring is con- 

 sidered to extend from 21 March to 20 June, summer 

 from 21 June to 20 September, autumn from 21 Sept- 

 ember to 20 December, and winter from 21 December 

 to 20 March. In the south temperate regions, the timing 

 of spring and autumn, like that of summer and winter, 

 is reversed, while, of course, in the tropics such seasons 

 cannot be recognized. 



For definitions of other words used in this book 

 reference may be made to the glossary on p. 105. 



