EXTERNAL FACTORS ON THE SPAWN DATE 



127 



Q. How do you know that? 



A. Because, although it was warm enough, they did not spawn. 



One has to break through this somehow. 



If in a fairly small area with a climate that does not differ much from 

 one part to another, one set of frogs spawn, it seems reasonable to 

 suppose that the breeding season has begun. To assume after this date 

 that some other set of frogs is not physiologically ripe is a form of 



o 



|9?6FEB 6 

 YEAR-DAY 



11 16 21 26 3 8 13 18 23 28 

 42 47 52 57 62 67 72 77 82 87 



Fig. 29. Chart Showing Maximum and Minimum Temperature, 



Maximum and Minimum Humidity, and Rainfall for February and 



up to the Last Date of Spawning in the Area Within 50 Miles of 



London, for the Year 1926 



Note that this year was early, and that February was wet. The spawning 

 season itself was dry. Note also that much of the spawning took place in a 

 period of falling temperature. In this and other charts, the spawn records 

 are indicated at the top, each unit indicating one report. Rainfall shown is 

 that of the day that is indicated plus that of the previous night. 



Special pleading that ought not to be admitted without some defmite 

 justification. With this in mind, it can easily be seen from the charts 

 (Figs. 29-32) that although sometimes spawning takes place in warm 

 weather, or after a period of rising temperatures, it does not always do 

 so. For example, there was considerable spawning during the cold 

 weather between 7th and 17th March 1928, when the temperatures 



