22 



THE EGGS OF MAMMALS 



jections of pituitary and pregnancy urine extracts, but no 

 ova were ever produced in the injected animals. 



That the early stages of ovogenesis in adult ovaries are 

 scarcely under the control of pituitary hormones is abun- 

 dantly evident from observations made upon the ovaries 

 of hypoph3^sectomized animals. Smith (1930) noted that in 

 completedly hypophysectomized rats no new large folUcles 

 or corpora lutea develop, but the proliferation of young 

 follicles goes on unimpaired for many months after hypoph- 

 ysectomy. Swezy (19336) has presented quantitative meas- 

 ures of the rate of ovogenesis in hypophysectomized rats, 

 and her data indicate that a larger number of young ova 

 may be produced in hypophysectomized females than in 

 normal non-pregnant animals. In Table I is presented a 

 suEMnary of her findings. 



TABLE I 



Numbers of Ova, Follicles axd Corpora Lutea in a Single Ovary of 

 THE Rat during the Oestrus Cycle, Pregnancy and Pseudopreg- 

 NANCY, and after Hypophysectomy AND THYROIDECTOMY. (From Swezy, 

 19336) 



* Persisting old corpora. 



Swezy concluded from these data that there is a basic 

 rate of ovogenesis which is observed in hypophysectomized 

 animals. That the increased number of ova in hypophysec- 

 tomized animals is due to an increased rate of production 

 and not merely to accumulation is proven by the absence 

 of any unusual number of degenerated ova. This rate is 



