EXPERIMENTALLY PRODUCED EXTRAUTERINE PREGNANCY. 69 



especially our previous observations concerning the partheno- 

 genetic pregnancy in the ovary of the guinea pig demonstrate/ 

 the development of the embryonal placenta preponderates re- 

 latively very much over that of the embryo proper, probably 

 because as I have already suggested, in contact with the host 

 tissue the derivatives of the ovum produce mainly the placental 

 structures. This is very marked in the case of the partheno- 

 genetic development in the ovary of the guinea pig, where in 

 typical cases under those conditions placental structures are 

 found exclusively and only exceptionally the embryo proper 

 begins to develop. 



These observations explain apparently very well the fact, that 

 while in the guinea pig a further going development of the ovum 

 is possible after extrauterine fixation, in man a complete extra- 

 uterine development is not an infrequent occurrence. Our 

 findings suggest as one of the causes for this difference in occur- 

 rence of extrauterine pregnancy in man and guinea pig, the fact 

 that in the case of man the host tissue offers a more suitable 

 soil than in the case of guinea pig; while as we saw in the latter 

 the development of the decidua in response to various kinds of 

 stimuli takes only place in the connective tissue of the uterine 

 mucosa, in the case of man the connective tissue of various pelvic 

 organs and even the appendix is able to produce decidua as many 

 observations show. In accordance with this interpretation a 

 number of observers actually reported the development of a 

 decidua in the fallopian tube in cases of tubal pregnancy. It is 

 very probable that in tases of tubal pregnancy in which a decidua 

 was not found in the tube, we had to deal with stages in which 

 the chorionic wandercells had already penetrated deep into the 

 host tissue and thus gradually destroyed the decidua ; in a similar 

 manner in the case of the guinea pig it can readily be seen that 

 the wandercells of the embryonal placenta destroy a greater 

 part of the decidua. It is very probable that from a certain 

 stage of embryonal development on, the decidua is no longer in- 

 dispensable as far as the continued existence and further develop- 

 ment of pregnancy are concerned. 



> Roux's Archiv, Bd. XXXII., p. 662, 1911; Zeitschriflf. Krebsforschung, 11. Bd.. 

 2. Heft, 1912. 



