18 THE EGGS OF MAMMALS 



ovarian tissue might very well be lost and the loss not 

 noticed upon serial sectioning (see Figure 5). Heys' results 

 can scarcely be due to chance alone, the difference in regen- 

 eration incidence between the young and older rats being 

 3.43 times the standard error of the difference, i.e., the odds 

 are over 3000 to 1 against this being a chance difference. 



It is clear, therefore, that regeneration of ovogenetic tissue 

 from somatic tissue is improbable in mammals. And cer- 

 tainly the definitive ova are normally not recruited from 

 somatic cells. We must turn to other experimental pro- 

 cedures to obtain some insight into the processes that lead 

 to the birth of ova in normal functional ovaries. 



The simple observation that unilateral ovariectomy or 

 incomplete total ovariectomy leads to a compensatory hyper- 

 trophy of the remaining tissue has led to a long series of 

 researches which, often incidentally, form the basis for our 

 modern knowledge of the elements of ovarian dynamics. 

 The fact that such hypertrophy occurs was originally estab- 

 lished both clinically (Robertson, 1890; Gordon, 1896; Sut- 

 ton, 1896; Morris, 1901; Doran, 1902; Kynoch, 1902; and 

 Meredith, 1904) and experimentally (Kanel, 1901; Bond, 

 1906; Carmichael and Marshall, 1908). An almost exact 

 doubling of weight in the remaining ovary of unilaterally 

 ovariectomized rats has been reported by Stotsenburg (1913) 

 and Hatai (1913, 1915) and the number of eggs shed is 

 demonstrably equal to the number normally produced by 

 two ovaries (see Lipschiitz, 1924; Hanson and Boone, 1926; 

 Crew, 1927; and Slonaker, 1927). In the opossum Hartman 

 (1925) has reported a tripling of the weight of the remaining 

 ovary and a similar threefold increase in the number of eggs 

 shed. In the rabbit (Asdell, 1924; Hammond, 1925; Lip- 

 schiitz, 1928) and the cat (Lipschiitz and Voss, 1925) a 

 single remaining ovary or even small ovarian fragments 

 produce the typical adult number of ripe follicles and eggs, 

 but an exact compensatory hypertrophy of ovarian tissue 

 is not so evident. Emery (1931) in a large series of uni- 

 laterally ovariectomized rats found not a doubling in weight. 



