Discussion 55 



last the entire reproductive lifetime of the animal. And this in spite of 

 the fact that is well known that the loss of the ova at each reproductive 

 cycle is very much larger than the number of eggs that come to ovula- 

 tion. My estimate was that somewhere between 100-200 eggs underwent 

 follicular development during each cycle, of which two to six, at most, 

 ovulate, and the remainder become atretic at the period immediately 

 following ovulation. And it was the process of that atresia that led me 

 to wonder as to its mechanism, because it is a very startling thing that 

 almost instantly after ovulation, nuclear changes overtake practically 

 all of the unovulated eggs. I have also found that, if at any stage in 

 the cycle one injected gonadotrophins, abnormal maturation divisions 

 were induced by the treatment, and that the fate of the eggs, so altered, 

 went on through this characteristic form of atresia. 



The phenomenon of Loeb's that Prof. Zuckerman mentioned is a very 

 common one in the guinea pig. In serial sections through both ovaries 

 of many hundreds of guinea pigs, I have found these masses, which 

 Loeb interpreted as parthenogenetic development of the eggs, to be 

 extremely common. It is a phenomenon which occurs so widely that 

 I quite agree with you it cannot be ignored in attempting to estimate the 

 origin of the various cells that one sees. 



Comer: I find myself in complete agreement with Dr. Dempsey. My 

 own direct experience with this problem is limited to a conscientious 

 effort, made over more than thirty years of study of serial sections of 

 mature monkey ovaries, to see whether I could discover any sign of 

 change of the cell of the germinal epithelium, or anything else, into an 

 oocyte. This has been a complete failure. I have completely failed to 

 see any convincing production of oocytes in mature monkey ovaries. 

 This is in spite of Swezy's account based in some part on some mis- 

 interpreted specimens from one of my papers. I do not think she ever 

 saw the specimens ; she worked from my figures only. 



In the recent work of Van-Eck done in part on some of the materials 

 borrowed from me, there seems to me a possibility of a fundamental 

 error. She tried to wipe the slate off, so to speak, by irradiating 

 the ovaries and then used deductions about the growth of follicles 

 immediately thereafter, without apparently realising the possibility that 

 the irradiation had done something to those follicles which grow and 

 degenerate in the next few days or weeks. So there again I find myself 

 fully in doubt as to the neogenesis of ova. 



Zuckerman: I think the flaw in the Van-Eck papers is really a serious 

 one. Van-Eck has assumed, in the first instance, that the atretic 

 phenomenon which occurs after irradiation is identical with natural 

 atresia. Because you can destroy an oocyte quickly with X-rays, she 

 therefore assumes that you can tell exactly how long it takes for an 

 ordinary oocyte to disappear under natural circumstances. There is no 

 reason for supposing that the two processes are identical. 



Parkes: There is one question I would like to ask. In this connection, 

 the definitions of the expressions pubertal, postpubertal and pre- 

 pubertal seem to be fundamental. What constitutes puberty from the 

 point of view of regeneration of oocytes ? 



