16 THE EGGS OF MAMMALS 



sulated rat and mouse ovaries, or even after careful excision 

 to drop very small crushed fragments. A number of in- 

 vestigators have therefore repeated Davenport's experiments 

 using extreme operative precautions, in some instances going 

 to the trouble of making serial sections of the extirpated 

 ovaries in order to be certain of the completeness of removal. 

 In practically every instance the per cent of animals 

 showing return of oestrus symptoms or of detectable ovarian 



^X_J 



Fig. 4. Section through ovary of young 

 rat showing small, compact ovary. YF, 

 young foUicle; C, ovarian capsule. LL, 

 line of excision. (From the Quarterly Re- 

 view of Biology.) 



tissue has been much below that reported by Davenport. 

 Fallot (1928) found return of vaginal cornification in three 

 out of twelve ovariectomized rats within six to six and one- 

 half months after operation, and ovarian tissue was found 

 in two of these. Parkes, Fielding and Brambell (1927) 

 detected oestrus symptoms after operation in eleven out of 

 one hundred and twenty-one mice, identifying ovarian tis- 

 sue in eight of these eleven. Haterius (1928) also found 

 apparent regeneration in 10 per cent of the mice he ovari- 

 ectomized, and attributed the regeneration to incomplete 

 extirpation. Pencharz (1929) reported return of oestrus in 

 only three of 118 ovariectomized rats and mice, and demon- 

 strated by serial sections of the ovarian region that incom- 

 plete removal had been made in the case of these three. 

 Heys (1929 and 1931), in an extremely careful analysis of 



