50 THE EGGS OF MAMMALS 



the secretion of sub-ovulatory amounts of hormone from 

 the anterior pituitary. Finally, Pincus and Enzmann (1935) 

 found definite ovum maturation with as little as 34 the 

 minimal ovulating dose of maturity hormone. 



In the ovaries of rabbit does which have copulated and 

 then received pituitary injections within six hours after 

 copulation the writer has observed the accelerated ripening 

 of a new set of follicles and the formation of the first polar 

 body. In these rabbits no accessory ovulation occurred 

 though the pituitary extract dosages were at least two to 

 three times greater than those necessary to cause ovulation 

 in unmated does. The absence of ovulation indicates pre- 

 sumably that the expulsion of ova can occur only from full 

 sized follicles, whereas the activation processes may be in- 

 itiated in ova whenever a sufficiency of pituitary hormones 

 are available. It should be neted, however, that the nuclear 

 activity occurred only in medium sized follicles and never 

 in follicles without antra or with small antra forming. Since 

 the ovum in the rabbit grows to some extent after antrum 

 formation (see Figure 11) it is possible that functional matu- 

 rity is attained at some time after antrum formation. A new 

 crop of follicles begins to mature in the mated rabbit, and 

 may certainly be stimulated to ovulate by the 4th day of 

 pregnancy as Wislocki and Snyder (1931) have demonstrated 

 by producing superfetation at that time with simultaneous 

 pituitary extract and sperm administration. It is evident, 

 therefore, that any attempt to dissociate in vivo the processes 

 involved in polar body formation and those involved in 

 ovulation depends in the mature rabbit upon hormone ad- 

 ministration during the very short interval of time following 

 copulation in the hope that active substances reaching the 

 medium sized follicles will differentially affect foUicular 

 growth and ovum maturation. 



Since the pituitary secretes a thyroid-stimulating as well 

 as a gonadotropic hormone it is possible that maturation 

 (and ovulation) is due directly to thyroid activity and only 

 indirectly to pituitary stimulation. Pincus and Enzmann 



