VARIABLE TEMPERATURES- 211 



transferred to 0° immediately after they had been laid and were 

 later removed to a favourable temperature (27° to 37°) they 

 developed more rapidly than the controls which remained at the 

 higher temperature. This acceleration was progressively main- 

 tained up to a period of 240 days at the low temperature. Longer 

 exposure resulted in only slight further acceleration. Kept at 

 37°, the eggs hatched in forty-six days. When placed at 0° for 

 thirty days and subsequently transferred to 37° they hatched in 

 thirty-seven days. There was progressive acceleration up to 240 

 days at 0°, after which they hatched in eleven days at 37° (Table 

 II.). It might be argued that 0° is above the threshold of develop- 

 ment and that growth was going on all the time, but as a matter 

 of fact the threshold is above 8°, so that the result obtained is only 

 to be explained as acceleration. 



Table II. Development of Grasshopper Eggs at Higher 

 Temperatures following an Exposure to 0° C. (from Parker). 



Days taken for hatching at temperatures given 



The reason for the accelerative effect of exposure to low tempera- 

 tures is obscure, and several hypotheses have been advanced to 

 account for the phenomenon. For instance, it has been suggested 

 that definite protoplasmic rhythms occur as regards susceptibility 

 to their influence, which express themselves in subsequent 

 acceleration of growth. Also the view has been advanced that 

 protoplasm is highly adapted to variable conditions as a normal 

 environment, whereas constant temperatures are abnormal and 

 tend to retard development. As Peairs has remarked, this would 

 interpret differences in growth rate as a retardation due to 

 constant temperature rather than as acceleration resulting from 

 temperature variation. Carothers (1923) showed that the eggs of 

 the grasshopper Circotettix do not hatch normally under laboratory 



