142 A. D. LEES 



all. Yet both sets came from the same breed and no differences 

 in external conditions seemed to exist. 



Lees: I can think of no convincing explanation for the type 

 of variation you mention. But I would like to call attention to 

 the recent work of Burges on the same species. Larvae, which 

 from their low respiratory rate would be judged to be in dia- 

 pause, nevertheless still moult at intervals. In the process they 

 often become smaller. 



Reinhold : Is there not a parallelism between the waking from 

 diapause and the stimulation or fertilisation of sea-urchin eggs? 

 The unfertihsed eggs, for example, have a respiration not 

 sensitive to cyanide, and become sensitive to cyanide on fertili- 

 sation. 



Lees: Yes, I think you could call the unfertihsed egg a dia- 

 pausing egg. 



Muehsam: You mentioned a case of the influence of neuro- 

 secretory brain cells on oviposition, where the cutting of the 

 axons resulted in oviposition in an unfed adult. On which 

 insect was this experiment done? 



Lees: On Oncopeltus. Johansson has shown that in the fasting 

 insect the brain inhibits the corpus allatum through the com- 

 missures. When these are cut, the inhibition ceases and egg- 

 laying begins. There is, of course, much variation according to 

 species. For example. Ellen Thomsen has shown that quite a 

 different mechanism is in control of egg maturation in Calliphora. 



Harpaz: I would like to draw an analogy becween the 

 breaking of diapause in insects and dormancy in seeds, referring 

 to the mechanism of mechanical injury. There is evidence from 

 Theron that the diapausing codling moth larvae in a cocoon 

 repair the cocoon even if the latter is torn several times, but 

 finally the insect gives up. pupates and resumes its development. 

 This could provide an analogy to mechanical injury in seeds. 



Lees: These experiments were repeated by Andrewartha in 

 Cambridge who did not succeed in breaking diapause by 

 removing the cocoon. This was, of course, an English strain not 

 a South African one, as in Theron's case. 



