SYMMETRY REVERSAL AND MIRROR-IMAGING 167 



Christina (colored), are declared to have had situs 

 inversus of at least the heart. One of the famous 

 Siamese Twins is stated to have had a partial reversal 

 of viscera. 



A few significant conclusions may be stated in re- 

 viewing the matter of symmetry reversal in human twins : 



a) The con- 

 dition is obvi- 

 ously associated 

 with a form of 

 twinning in 

 which the two 

 individuals are 

 derived from a 

 primordium 

 that would nor- 

 mally produce 

 the right- and 

 left-hand halves 

 of a bilateral in- 

 dividual. 



h) The left- 

 hand individual 

 always retains 

 the normal situs 

 and the right-hand individual very commonly shows 

 some degree of symmetry reversal. 



c) It is very rare indeed that separate human twins 

 show any signs of situs inversus viscerum, but they do 

 not uncommonly show mirror-imaging in certain minor 

 external characters such as finger-prints (see The Biology 

 of Twins, pp. 159-60). 



Fig. 56. — The viscera of the double monster 

 shown in Fig. 55, laid out in somewhat schematic 

 fashion to show the complete sikis inversus vis- 

 cerum. (From Morrill.) 



