56 Discussion 



Zuckerman: In the context of oogenesis the term varies according to 

 species. If, for example, it is true that the lemurs can produce oocytes 

 when sexually mature, I would be inclined to say that they constitute 

 one extreme in a range of mammals, the other being those species which 

 achieve their entire complement of oocytes before birth. In the case of 

 the rat we know that nuclear configurations of the kind which could be 

 interpreted as oogenesis cease to appear after about day 4. Some people 

 put it even earlier. 



Parkes: That is long before the first ovulation? 



Zuckerman: Yes, but even so it would not surprise me to find a few 

 oocytes being formed later. 



Huggett: Tell me, have you any knowledge as to where these oocytes 

 come from? 



Zuckerman: I have always assumed that it was true that the gono- 

 cytes migrate into the embryo. Bounoure, Regan, Wolff and Nieuwkoop 

 have studied the problem, and their results show that the gonocytes 

 migrate to the genital ridge. The gonocytes become "fixed" there in 

 some sort of way ; they multiply ; and when they cease multiplying they 

 become differentiated into oocytes. 



Corner: Hurdig has been able to mark, in human embryos, the gono- 

 cytes with one of the microchemical stains — a lipophosphatase. This 

 seems to be quite clear. Do you not think it is quite believable work and 

 that this corroborates the old story? 



Strauss: Is it possible for the neoformation of oocytes in the adult 

 mammal to be a question of comparative embryology as well as one of 

 a cytological nature? 



Zuckerman: In what sense embryological ? 



Strauss: In the lower archaic mammals, like the Galago and Dasypus, 

 you will find some neoformation. Gerard, as well as Hamlett, claims to 

 have seen neoformation in these primitive mammals, in as distinct a 

 manner as one could wish. 



Zuckerman: All these creatures started off on their reproductive life 

 as mammals, and as far as we know as far back as the palaeocine. They 

 have continued and evolved quite successfully until now, a few fading 

 out. I do not think we have any reason to regard the Galago as being 

 more archaic than the rest, and that postpuberal oogenesis constitutes 

 a primitive phenomenon. 



Matthews: In fishes, of course, there is entirely new production of 

 oocytes, but I don't know what happens in the bird. 



Parkes: Prof. Zuckerman, can you say whether or not endocrine 

 activity on the part of the ovary continues after the destruction of the 

 oocytes and, therefore, of the follicular system, and if so for how long? 



Zuckerman: I can only give you the facts for experiments on rats 

 which we have done. Including litter-mate controls, 306 rats from 76 

 litters were used. The ovaries were directly irradiated after being ex- 

 teriorized (the rest of the body being shielded), at a dose about four 

 times higher than the lethal dose when the beam is applied to the body 

 surface. Complete sterilization was judged by the absence of a single 

 recognizable oocyte in serial sections. Most animals entered a phase of 



