CYCLIC CHANGES IN UTERES AND OVARIES, 43 



in this effect. We are testing this suggestion still further at the 

 present time. 



12. A description of the signs of heat is given in accordance 

 with the observations of the breeder, Miss A. E. C. Lathrop. 



13. After total extirpation of the ovaries, the uterine mucosa 

 becomes similar to the mucosa of the pregnant uterus in a non- 

 pregnant horn; gradually an atrophy of the different layers of 

 the uterine wall takes place. If we extirpate the ovaries soon 

 after ovulation the effect is the same as if the corpora lutea are 

 extirpated at that period, as far as the predecidual proliferation 

 in the connective tissue and the accompanying changes in the 

 epithelium which take place between the fourth and seventh day 

 are concerned. As far as this effect is concerned the corpus 

 luteum is the active part of the ovaries. While, however, ex- 

 tirpation of the corpora lutea does not prevent those uterine 

 changes which accompany heat and does not prevent a new sexual 

 cycle, extirpation of the ovaries prevents all cyclic changes in 

 the uterus. 



14. Early extirpation of the corpora lutea within the first forty 

 hours after copulation prevents in a similar manner the develop- 

 ment of experimental placentomata as an early extirpation of 

 the ovaries. If the ovaries are removed six to eight days after 

 copulation and at the same time incisions are made into the uterus, 

 either none, or only very small placentomata develop and the 

 developing placentomata die at an earlier date than they would 

 have done otherwise. An extirpation of the corpora lutea six 

 to seven days after copulation also causes the developing pla- 

 centomata to be smaller. If under these conditions an ovum 

 develops in the incised uterus within the decidual tissue, the 

 development of the ovum is usually much retarded. A similar 

 retardation of the development of the ovum we observed in a 

 case of experimentally produced extrauterine pregnancy in the 

 guinea-pig. If the ovaries are extirpated two days after the 

 making of the incisions the developing placentomata are usually 

 smaller. Castration done at a time when the placentomata 

 had already reached a considerable size causes an acceleration 

 in the necrosis of the placentomata. Castration does however 

 not prevent regenerative changes in the uterine mucosa. 



