42 LEO LOEB. 



lutea leads in the large majority of cases to an acceleration of 

 the next ovulation. Certain conditions, however, may prevent 

 the early ovulation. In the latter cases the structure of the 

 uterus corresponds to the late stage of the sexual cycle. If 

 however a new premature ovulation is brought about through 

 the extirpation of the corpora lutea, a new cycle starts in the 

 uterus at the time of the accelerated ovulation. Mature follicles, 

 or possibly other follicles, are in the absence of corpora lutea able 

 to call forth the structural changes in the uterus accompanying 

 heat and the rupture of the follicles and development of corpora 

 lutea is followed by the typical uterine cyclic changes. 



10. We stated previously that also during pregnancy extirpa- 

 tion of the corpora lutea is followed by an early ovulation. While 

 thus pregnancy in itself does not prevent an ovulation to take 

 place (only the corpora lutea persisting during pregnancy pre- 

 venting the ovulation) pregnancy does prevent the cyclic changes 

 of the uterus preceding, accompanying or following ovulation; 

 during pregnancy the uterus retains its resting condition not- 

 withstanding ovulation. This influence of pregnancy is not a 

 mechanical one, inasmuch as it is found in the non-pregnant 

 horn as well as in the pregnant horn in cases in which a pregnancy 

 developed only in one horn. The presence of a necrotic placen- 

 toma or the occurrence of an abortion does not prevent the cyclic 

 changes in the uterus that set in with ovulation. 



11. If five to seven days after copulation both horns of the 

 uterus are split lengthwise and the development of a normal 

 pregnancy is prevented, ovulation is delayed under those con- 

 ditions; it occurs between the twentieth and thirtieth day after 

 the previous copulation, even in cases in which a developing 

 embryo could not be seen in the placentomata growing at the 

 site of the incisions. On the other hand in a case of an experi- 

 mentally produced extrauterine pregnancy degeneration of the 

 corpus luteum and a new ovulation were not delayed notwith- 

 standing the presence of living embryonic (including placental 

 structures of embryonic origin) in the animal. These observa- 

 tions suggest that it is primarily the life of the maternal part of 

 the placenta which prevents the new ovulation during pregnancy 

 and that the embryonic structures are only indirectly concerned 



