EXPERIMENTALLY PRODUCED EXTRAUTERINE PREGNANCY. 73 



relatively large number of guinea pigs, leading in the first place to 

 the formation of placental structures, in some cases however also to 

 the formation of embryos in the stage of the germ layers. We have 

 discussed the possible causes for this parthenogenetic develop- 

 ment on another occasion.^ We have perhaps to deal with a 

 development which is caused by changes in the circulation and 

 in the exchange of gases at the time and in consequence of the 

 rupture of follicles. 



Such an explanation would be in accordance with the fact that 

 the first segmentations of the ovum in the ovary of the guinea 

 pig are found especially in atretic follicles, that the segmentations 

 set in with beginning atresia and then gradually progress. Now 

 we know that the atresia of follicles is more marked, than at any 

 other time, at the time of ovulation.^ In this connection it is 

 especially worthy of notice that the first segmentations of the 

 ova in the ovary as well as the furthergoing parthenogenetic 

 development, which leads to the formation of embryonal and 

 placental structures, is preferably found in the ovaries of young 

 animals. The latter, however, occurs occasionally also in some- 

 what older guinea pigs. In such cases we may perhaps have to 

 deal with structures which originally developed in younger an- 

 imals, which then however had remained stationary for a longer 

 period of time. 



We have still to discuss the significance of these structures for 

 the interpretation of certain pathological formations, namely the 

 embryomata and the chorion epitheliomata of the female germ 

 gland. The large majority of pathologists assume in agreement 

 with the suggestion of Bonnet and Marchand that these patho- 

 logical structures take their origin from misplaced blastomeres 

 and not from the parthenogenetically developing ovum. As I 

 formerly emphasized^ our observations make it very probable 

 that such pathological formations originate from parthenogenetic- 

 ally developing ova. They are therefore the "descendants" and 

 not the "brothers " of the organism in which they originate. We 

 may assume that in certain cases the parthenogenetic develop- 



1 Leo Loeb, Proceedings Am. Philosophical Society, Vol. L., p. 228, 191 1. 



2 Leo Loeb, Journal of Morphology. 



' Zeitschrift f. Krehsforschung, loc. cit. 



