276 J. Maynard Smith 



Table III 



Expectation of life in days of females kept at 20° c. 



temperature prolongs life because it slows down the rate of 

 egg-laying. 



This suggestion has been confirmed by experiments using 

 virgin females (which lay eggs at a reduced rate), and females 

 lacking ovaries. The latter were obtained by using females 

 homozygous for the mutant " grandchildless " (Spurway, 

 1948), whose offspring appear to be normal in all respects 



Table IV 



Expectation of life of femai.es kept at 20° c. 



