Early Stage of Extrauterine Pregnancy. 105 



uterine cavity through the incision made in the uterus two days, 

 sixteen hours after copulation. The ovum migrated around the 

 peritoneal covering of the uterus and embedded itself superficially 

 in the connective tissue of the peritoneum. Here it developed 

 and is still developing at the times of examination, as the existing 

 mitoses indicated. It produced certain placental structures which 

 joined the surrounding connective tissue and blood vessels. It is 

 not very probable that an ovum leaving the ovary at the time of 

 the last ovulation three days ago could within so short a period of 

 time produce these structures after the passage through the tubes. 

 In this case we would have to deal with parthenogenetic develop- 

 ment of the ovum. It is very much more probable that we have 

 to deal with the extrauterine fixation and development of an 

 ovum leaving the uterine cavity through the incision made a few 

 days after the previous ovulation, the cut in the upper part of 

 the uterine horn having been made exactly at the time when the 

 ovum was approaching the uterus after its passage through the 

 fallopian tube. In this case we would have to deal with a very 

 slow and very much delayed development of the embryo, due to 

 the unfavorable conditions under which the ovum develops. 



These findings are of importance: first, because they confirm 

 our previous findings, that connective tissue other than that of 

 the uterine mucosa is unable to produce decidua in the guinea pig. 

 While it is under these unfavorable conditions possible for an 

 ovum to undergo the early stages of development, lack of the 

 proper response on the part of the host tissue (lack of decidual 

 reaction) renders the development of the later stages of extrau- 

 terine embryonal development impossible. 



2. In contact with the connective tissue and vessels of the 

 host the ovum develops mainly certain parts of the fetal placenta, 

 namely syncytia and plasmodia and layers of small cuboidal cells. 

 These structures correspond to certain parts of the normal pla- 

 centa of the guinea pig which lie in the periphery of the embryo 

 and enter under ordinary conditions into relations with the 

 maternal part of the placenta. Certain parts of the trophoblast 

 and the embryo proper develop only in a rudimentary manner 

 under these conditions. 



3. The embryonic and placental structures developing outside 



