Rate of Ageing in Drosophila suhohscura 277 



except for the absence of gonads. The results of these experi- 

 ments are shown in Fig. 3 and Table lY. As before, the 

 exposure of normal mated females to a high temperature 

 increased their expectation of life at 20°. As would be ex- 

 pected from the hypothesis being tested, both virgin and 

 ovariless females lived for longer than did the controls, and 

 closely resembled the females exposed to a high temperature. 

 The final confirmation of the hypothesis comes from the fact 



16 24 32 40 48 56 64 72 80 88 96 104 112 120 

 Age in days 



Fig. 3. Survival time of females at 20°. A, normal mated 



females; B, ovariless females; C, normal virgin females; 



D, normal mated females exposed for 5 or 6 days to 31°. 



that the expectation of life of ovariless females, as of males, 

 is not increased by exposure to a high temperature ; since such 

 females will not lay eggs in any case, exposure cannot further 

 prolong their life. The greater longevity of virgin as com- 

 pared to mated females has previously been demonstrated by 

 Bilewicz (1953) in Drosophila melanogaster, and by Griffiths 

 and Tauber (1942) in Periplaneta americana. 



It is natural to suppose that the causes of ageing of ovariless 

 or virgin females at 20° are the same as the causes of ageing of 

 males at the same temperature. But these experiments leave 

 one question unanswered. Does egg-laying shorten the life 



