250 STUDIES ON PATHOLOGIC OVA. 



rather than to hasten the expulsion of the dead mate. That is, the survival of one 

 twin, especially in the earlier stages of development, may depress rather than 

 enhance the factors that lead to abortion. 



The impulses arising from the presence of the dead fetus may be counter- 

 balanced or offset, for a time at least, by the presence of the living fetus, and thus 

 tend to prolong the status quo. This would be the case particularly whenever, as 

 in the specimen donated by Dr. Ross, the two chorionic vesicles are fused into a 

 single mass; for then the portion belonging to the dead fetus, even if it forms one- 

 half of the combined mass at first, soon is outstripped in size by the surviving 

 vesicle, which, in the absence of infection, may continue to grow quite undisturbed, 

 for some time at least; and even in the case of infection of the dead vesicle, prompt 

 invasion of the living does not necessarily occur. Aside from clinical experience, 

 this was indicated also by the experiments of Maffuci (1894) on incubating eggs 

 and on pregnant rabbits and guinea-pigs. The apparent resistance of the young 

 fetus to syphilis, the characteristic lesions of which have not as yet been success- 

 fully demonstrated in fetuses much before the second half of pregnancy, would 

 also seem to point in the same direction. 



From these considerations it would seem to follow that especially favorable 

 conditions for the production of gross differences would exist in some cases of 

 twin pregnancy. Hence it need not surprise us that these differences have been 

 largely responsible for the quite general belief in the occurrence of superfetation 

 in women. But at present it remains merely a possibility, for the evidence on 

 which this belief rests is wholly inadequate. It is interesting to recall that, in 

 the past, fetus papyracei have also been regarded as examples of superfetation, 

 as illustrated by the specimens reported by Fasola (1887). 



DESCRIPTION OF PLATE. 

 PLATE 14. 



FIGS. 141-142. Hydatiform villi from No. 2250a and 6, shown in fig. 134, plate 12, Chapter VIII. X4. 



FIGS. 143-144. Twin conceptuses, both with hydatiform chorions. No. 241 lo and 6. (See Chap. VIII.) X1.35. 



FIG. 145. Enlarged fetus from same, showing maceration effects. X2. 



FIGS. 146-147. Macerated hydatiform villi from the same case. X6. 



FIG. 148. Cyema covered with magma. No. 1771. (See Chapter IX.) X2.67. 



FIG. 149. Apparent superfetus from a cat. (After Harman.) 



FIG. 150. Macerated, distorted normal cat fetus 10 mm. long. (After Kunz.) 



FIG. 151. Slightly macerated twin fetus. No. 1840o. X 11.35. 



FIG. 152. Pseudosupcrfetus. No. 18406. X2.67. 



FIG. 153. Opened, everted vesicle of No. 1840a and incised vesicle of 18406. X0.66. 



FIG. 154. Opened chorionic vesicle of 18406 and placcntal area of 1840a. X0.66. 



FIG. 155. Twin fetus. No. 20366. X0.66. 



FIG. 156. Pseudosuperfetus, No. 2036o, disarticulated by maceration. X2. 



