154 



THE PHYSIOLOGY OF TWINNING 



acormi, are, perhaps, 

 the most bizarre ex- 

 amples of human 

 teratoma. Schatz de- 

 scribes considerable 

 numbers of such mon- 

 strous types in great 

 detail and in each case 

 suggests, on the basis 

 of a study of body and 

 placental vascular 

 conditions, the prob- 

 able cause of each. 

 These are matters too 

 far removed from our 

 present interest to war- 

 rant discussion here. 



Up till now we have 

 confined our attention 

 to conditions in en- 

 tirely separate human 

 one-egg twins. It now 

 remains for us to make a brief survey of conditions in 

 human double monsters or conjoined twins. 



Fig. 54. — A very abnormal human 

 twin fetus which has resulted from early 

 heart-death and has developed badly 

 owing to the paucity of the borrowed 

 blood supply from the "favored" twin. 

 Such a twin is practically unrecognizable 

 as a human creature and is an acardius 

 amorphus. (After Schatz.) 



CONJOINED TWINS 



ON THE INFLUENCES WHICH CONJOINED TWINS 

 EXERT UPON EACH OTHER 



Just as in separate human twins one individual may 

 be smaller in size or defective in various ways, so in 

 conjoined twins the component individuals may be very 

 unequal in size and normality of structure. 



