i66 



THE PHYSIOLOGY OF TWINNING 



departures from the normal situs solitus are to be inter- 

 preted as evidences of incomplete symmetry reversal. 

 Complete situs inversus in separate one-egg twins is 

 rare; but one conspicuous instance has come to my 

 attention. This is the case of Kuchenmeister (1883) 

 who describes a pair of nearly full-term twins one of 



which had complete situs 

 solitus, the other complete 

 situs inversus. 



In this place it is not my 

 purpose to present any large 

 amount of data on situs 

 inversus viscerum in human 

 twins. Morrill (19 19) has 

 recently given us a concise 

 survey of the literature on 

 this subject. He himself has 

 made a detailed study of a 

 double-headed monster that 

 came to his attention and 

 has figured the monster in 

 its entirety (Fig. 55) as well 

 as its visceral conditions 

 (Fig. 56). This is obviously 

 a case of complete situs in- 

 versus viscerum and is of very great interest. Morrill 

 calls attention to the existence of situs inversus in the 

 cases of several rather famous diplopagi. Eichwald 

 states "that the thoracopagous monsters examined by 

 him showed, in almost every case, some transportation 

 of the viscera in one of the bodies, though to a vary- 

 ing extent." The pygopagous CaroHna twins, Millie- 



FiG. 55. — A striking example 

 of a human double monster 

 (anadidymus) which had per- 

 fect siius inversus viscerum. 

 (After a photograph published 

 by Morrill.) 



