ALLEGED OCCURRENCE OF SUPERFETATION. 249 



4 diameters, is abundant evidence of the fact that it died a considerable period of 

 time before the abortion occurred. This interval must have been several weeks. 

 This specimen also nicely illustrates the fact that the death of one fetus does not 

 necessarily result in the immediate abortion of it and its vesicle or of the other 

 chorionic vesicle, as is sometimes still assumed. 



Through the generosity of Dr. Gustetter, I am also enabled to present repro- 

 ductions of the fetuses spoken of in his article. They are shown in figures 155 and 

 156 and from these illustrations it is clear that the smaller of the 2 fetuses 

 probably stopped growth at about the sixth week. After this it became macerated 

 and finally disintegrated, while the larger continued to grow, as in case of the speci- 

 men from Dr. Ross. The larger of these fetuses is practically normal in appearance 

 except for the post-partum shriveling. It is approximately 100 days old. 



Other specimens in the Carnegie Collection, such as No. 2036 a and 6, well 

 might be included here, for one fetus was grouped as normal and the other as 

 macerated. Indeed, it is a not very rare occurrence to find that the fetuses in a 

 twin pregnancy had to be placed in different groups by Mall and his associates at 

 the Carnegie Laboratory. However, this was not done because such specimens 

 were regarded as instances of superfetation, but because the fetuses, although of 

 the same age, differed in form and appearance. It is interesting that Saniter (1903) 

 also reported a case of two unequally developed tubal conceptuses, one of which 

 was implanted in the isthmus and the other near the fimbria. The former was 

 said to be only of the third to the fourth week, while the latter contained a 

 fetus 4 cm. long. Both chorionic vesicles were said to have ruptured freshly. In 

 commenting on this case of Saniter's, Werth (1904) said that he regarded the 

 question as to whether it was a case of superfetation or merely one of twin preg- 

 nancy an open one. 



It may be recalled that the occurrence of fetus papyraceus in cases of twin 

 pregnancy also has been attributed in the past to superfetation. Moreover, as 

 stated above, intrauterine death of one or more fetuses belonging to the same 

 litter is relatively common in some mammals. However, since Jenkinson (1913) 

 stated that the allantois and its blood-vessels and also the syncytium are regu- 

 larly retained at birth in some marsupials, to be absorbed later through the 

 activity of maternal leucocytes, it is evident that one must use caution in judging 

 on the basis of experience in other mammals, especially the lower ones. In some of 

 these the conditions are apparently quite different from those encountered in man. 

 Strahl and Henneberg (1902) also pointed out that in the mole the entire placenta 

 and membranes, as Hubrecht stated, are often retained for a month after parturi- 

 tion. No one would assert that the human uterus shows the same tolerance 

 or the same resorptive power, yet the daily experience of physicians, as well as 

 the literature in obstetrics and gynecology, is replete with instances of retention 

 of the membranes or the entire conceptus long after the death of the fetus. Al- 

 though the presence of a surviving conceptus in multiple pregnancy materially 

 alters the intrauterine conditions, it also would seem to predispose to retention 



