68 LEO LOEB. 



formation of decidua in the peritoneal connective tissue, the ovum 

 is likewise unable to do so.^ 



These observations furthermore clear up the fate of the ovum 

 in cases in which it is not able to develop normally in the uterine 

 wall. Frequently a fixation of the ovum does not take place in 

 such abnormal cases, especially on the smooth peritoneal epi- 

 thelium. In other cases however the ovum fixes itself and begins 

 to develop in the connective tissue without however finding the 

 necessary decidual reaction on the part of the surrounding con- 

 nective tissue. In such cases the development of the embryo 

 proper as well as of the embryonal placenta is very much re- 

 tarded as compared to the normal development; furthermore the 

 embryonal differentiation also remains incomplete and we may 

 assume, that after some time the growth ceases and the em- 

 bryonal structure is substituted by host connective tissue in a 

 similar manner as in the ovary of the guinea pig. We find there- 

 fore in the guinea pig no or only a very much retarded and in- 

 complete development of the ovum outside of the uterus. This 

 is in all probability due to the fact that the host tissue is not 

 suited to receive the ovum and to supply it with the necessary 

 food stuffs. In this case the host tissue behaves passively in 

 contradistinction to the uterine mucosa. This conclusion agrees 

 with the fact that we find a general parallelism in the ability 

 of the uterine mucosa to produce decidua or deciduomata and 

 to permit a normal development of the ovum. As I have previ- 

 ously shown, various experimental interferences, as for instance 

 extirpation of the corpora lutea or of the ovaries, have approxi- 

 mately to the same extent an inhibiting influence on the develop- 

 ment of deciduomata and of pregnancy. We may thus conclude 

 that the ability of the host connective tissue to produce a decidua 

 in a normal manner is of significance for the normal development 

 of pregnancy. 



We see therefore that in the guinea pig the ovum does either 

 not develop at all outside of the uterus or in case an extrauterine 

 fixation of the ovum should take place, the development is much 

 retarded and soon comes to a standstill. As our present and 



1 As we shall later especially emphasize, the same holds good in the case of the 

 parthenogenetic development of the egg in the ovary of the guinea pig. 



