130 Discussion 



Danielli: Yes, it is not that I am questioning the likelihood that Dr. 

 Miihlbock's is the right explanation. But it comes so close to being proof 

 that one would like to see the proof actually established. 



Parkes: Have you any idea of how smelling other individuals makes 

 them pseudopregnant ? 



Miihlbock: We think that it is a mechanism which is set in motion 

 once a certain level of stimulation is reached. Some centre in the nervous 

 system, which may be stimulated along several pathways, then releases 

 some factor which in its turn causes luteinizing hormone or something 

 like that to be released by the hypophysis. 



Danielli : There is a somewhat analogous situation in locusts connected 

 with the change from the solitary to the swarming phase. I am not sure 

 whether the mechanism has been really established there. I believe that 

 there is a certain amount of evidence that there must actually be contact 

 between the locusts; it is not sufficient that they see one another or 

 smell one another. 



Another point I should like to discuss is whether you really have worked 

 with homozygous strains. I should have thought that that was highly 

 improbable. It would mean that there were no hidden recessives in 

 your stock and that strikes me as being improbable. It does seem more 

 likely that you managed to get a certain number of strains in which 

 certain groups or sets of the genes turn up, are really viable, and other 

 sets of the genes, so to speak, die off in the early stages, resulting in death 

 in early embryonic stages or even before fertilization. Now, a situation 

 like that might lead to a strain in which most, if not all, of the animals 

 would be very closely similar in their genetic constitution, but there 

 is a big jump from that situation to one where a pair of animals is 

 genetically identical. 



Miihlbock: Would you agree with 99 • 999 per cent? 



Danielli: I would not agree with any numerical assessment unless you 

 had appropriate evidence. 



Bourne : You said that in your parabiotic experiments with the young 

 and the old, the old animal dies within a few months; does the young 

 animal die with him? 



Miihlbock: Yes, it does; but if you separate them the young one will 

 survive. 



