Discussion 285 



that egg production is at least one factor responsible for ageing in 

 Drosophila, but I have been unable to find any relation between 

 fecundity and age in egg-laying fishes. 



Hinton: In most flies when the ovaries ripen the abdomen swells 

 greatly, and the ripened ovaries occupy a considerable percentage 

 of the total volume of the abdomen. The other organ systems are 

 frequently much displaced by the ripened ovaries,which may account 

 for a high percentage of the total weight of the female. 



Maynard Smith: They are not so big in Drosophila. Eggs are 

 pumped through at a rate of about 30 or 40 per day, but the ovary 

 itself is never very large. 



Berg: Is the ovary a self-regulatory mechanism in the fly? A 

 selective effect on the ovary without aff'ecting hormonal regulatory 

 mechanisms would be unusual. 



Maynard Smith: What do 3^ou think the regulatory mechanism 

 might be here? The ovary is not itself a hormone producer, is it? 



Wigglesworth : One of the main detectable abnormal effects on the 

 insect of raising the temperature is the effect on hormone action. 

 You can get an insect which is apparently metabolizing normally, 

 but you knock out the action of the growth-promoting hormone. 

 The ovary certainly appears to have a hormonal influence, a sort of 

 feedback influence, upon the endocrine system. So that even in your 

 ovariless insects produced genetically you might be impairing their 

 endocrine system through lack of this feedback mechanism. 



Maynard Smith: The ovariless flies are the off'spring of females 

 homozygous for the mutant grandchildless, and the suspicion, which 

 is not adequately demonstrated, is that females carrying this gene 

 produce eggs without pole plasm. This would explain the fact that 

 the female off'spring have no ovaries and the male off'spring no testes. 

 If the ovariless females had lived for a shorter time than the controls, 

 I would have said something else was wrong too, but they lived 50 

 per cent longer. I was very reluctant to accept this simple mechani- 

 cal explanation, that they live longer because they do not lay eggs, 

 but everything seemed to fit in so well that until something does not 

 fit, I have to accept it. 



Kershaw : The overwhelming effect of ovaries and this relation to 

 nutrition has been shown in some experiments that we have done. 

 We have exactly the opposite results from those in your Drosophila. 

 In Aedes aegypti, which depends largely on blood meals, the virgin 

 females live for a much shorter time than the normal egg-laying 

 females (Lavoipierre, M. M. J. (1958). Nature (Lond.), 181, 1781). 

 This disparity would fit in with the complete dislocation of nutrition 

 invoked by the disturbance of normal ovarian function. 



