CHAPTER II 

 THE ORIGIN OF THE DEFINITIVE OVA 



A long-lived controversy concerns itself with the origin of 

 the definitive germ cells. Do they arise de novo from somatic 

 tissue in the sexually mature adult, or are they segregated 

 as primordial precursors early in embryogeny? Weismann's 

 theoretical considerations (1883, 1904, also Nussbaum, 1880) 

 on the continuity of the germplasm led initially to the active 

 investigation of this problem. In the light of modern the- 

 oretical genetics the strict interpretation of the Weismannian 

 dogmata is probably no longer necessary. For, since the 

 data of genetics indicate that every normal nucleus in the 

 organism contains the full complement of genes and that 

 somatic segregation of genes is a rare and exceptional phe- 

 nomenon, it is no longer necessary to postulate the trans- 

 mission of a special, unimpaired germ tissue. The problem 

 of the origin of the germ cells thus properly becomes one 

 concerned with the dynamics of embryonic differentiation 

 and peculiarly one of regeneration. In fact most of the 

 recent experimental approaches have been concerned with 

 the probability of the regeneration of germ cells from somatic 

 tissues. Able reviews of the general problem are contained 

 in the paper of Heys (1931) and the monograph of Harms 

 (1926). 



Since we are concerned specifically with the origin of the 

 definitive ova of mammals the question that we may set is 

 concerned less with general theory and more with pertinent 

 fact. We want to know what processes are responsible for 

 the emergence in the ovary of the functional eggs. 



We may at once distinguish two types of investigation. 

 The first, essentially descriptive, is concerned with the de- 

 velopment of the ovary and its germ cells from early em- 



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