28 THE EGGS OF MAMMALS 



animals) a stimulation to ovogenesis may be engendered by 

 the follicle stimulating hormone. Hisaw and his collab- 

 orators find that corporin (the hormone of the corpus luteum) 

 exerts effects on the ovary like those of the follicle stimulat- 

 ing hormone while oestrin decreases the secretion of follicle 

 stimulating hormone and stimulates luteinizing hormone 

 production from the hypophysis. Pregnant and pseudo- 

 pregnant animals may therefore exhibit an increase in ovo- 

 genesis due to direct action of corporin from their corpora 

 lutea, whereas animals in oestrus and those receiving oestrin 

 injections show reduced ovogenesis perhaps because of the 

 action of the induced luteinizing hormone secretion. 



It is obviously not possible to arrive at any final decision 

 concerning the factors governing ovogenesis until additional 

 pertinent data are available. The most concise summary 

 of the evidence indicates that ovogenesis occurs from the 

 germinal epithelium at a typical intrinsic rate which may 

 be reduced by the action of a hormone or hormones from 

 the anterior pituitary. But even this deduction requires 

 further verification in the form of careful quantitative esti- 

 mates of ovogenesis in its relation to atresia, and particularly 

 an inquiry into the nature of the atresia of young ova and 

 folhcles. We are completely unaware of the intimate nature 

 of the intrinsic proliferative capacity of the germinal epi- 

 thelium. How does it compare with the mitotic index of 

 tissues generally? Is it a self-perpetuating phenomenon in 

 the sense that the atresia of its products releases substances 

 stimulating cell division? We shall see for example that the 

 atresia of maturing follicles is often accompanied by the 

 formation of mitotic spindles and it is well known that 

 cytolized cell products (trephones) promote cell division. 

 An extraordinary variety of problems suggest themselves. 

 Patience and the formation of substantiated hypotheses will 

 result in their solution. 



In summating the evidence relating to the normal ovo- 

 genetic processes in prepubertal and post-pubertal animals 

 little doubt remains that the definitive ova are proliferated 



