452 GENERATION. 



fused into one. The instances on record, one of which we 

 have given, 1 of twins, one white and the other black, show con- 

 clusively that two ova may be developed in the uterus at the 

 same time. While there can be no doubt upon this point, the 

 question of the possibility of the development of two beings 

 from a single ovum remains unsettled. It is thought to be 

 more difficult to understand how two conjoined monsters, 

 like the celebrated Siamese twins, who have just died, could 

 be developed from two ova which became fused, than to 

 imagine the development of two beings from a single ovum. 

 This question, however, belongs to teratology, and could only 

 be settled by observations of conjoined monsters very early 

 in their development, which do not exist in literature. 



As pathological conditions, we have extra-uterine preg- 

 nancies, in which the fecundated ovum, forming its attach- 

 ments in the Fallopian tube (Fallopian pregnancy) or within 

 the abdominal cavity (abdominal pregnancy), undergoes a cer- 

 tain degree of development. The uterus usually enlarges, in 

 these instances, and forms an imperfect decidua. 



Cause of the First Contractions of the Uterus in Normal 

 Parturition. The cause of the first contraction of the uterus 

 in normal parturition is undoubtedly referable to some change 

 in the attachment of its contents, which causes the foetus and 

 its membranes to act as a foreign body. When, for any 

 reason, it is advisable to cause the uterus to expel its contents 

 before the full term of pregnancy, the most physiological 

 method of bringing on the contractions of this organ is to 

 cautiously separate a portion of the membranes, as is often 

 done by introducing an elastic catheter between the ovum 

 and the uterine wall. A certain time after this operation, 

 the uterus contracts to expel the ovum, which then acts as a 

 foreign body. 



In the normal state, toward the end of pregnancy, the 

 cells of the decidua vera and of that portion of the placenta 



1 See page 348. 



