440 Duplicate Twins and Double Monsters 



Summary of Friction-skin Conditions in Duplicate Twins. 



In the above cases the identity of palmar markings is much more com- 

 plete than is brought out by the formulae, since these last have an arti- 

 ficial element in their formation and the course of a line often depends 

 upon the detail of one particular ridge, one of Galton's "minutia;" 

 and since the correspondence, even in duplicate twins, is not carried as 

 far as these, a fact that will be brought out later together with the 

 probable reasons for it, it may easily happen that such a slight differ- 

 ence, when occurring at a critical point in the course of a main line, 

 may change the symbol of one or perhaps of two positions. Another 

 source of error is found in affixing a designation to the carpal region, 

 since a print often leaves off at the wrist before the limit of the friction 

 skin is reached, and thus in the case of a very low carpal triradius, this 

 latter may not even appear, causing the investigator to class as a parting 

 what should be a triradius. In the entire nine sets of true duplicates 

 there is not a single difference that cannot he traced to one of the above 

 sources and thus he shown to he of no real value. 



Features of especial interest in the palmar and finger configuration 

 of duplicates are (1) the tendency to a symmetry between the two sides, 

 which appears to be far greater than among other individuals, and (3) 

 the mysterious reversal of index patterns of one hand or the other. 

 Added to this last there seems also some tendency to lack of corres- 

 pondence in the thumb j^atterns, and in a single instance (the rights of 

 No. IX) there is a difference in the patterns of the middle fingers. 



A detailed comparison of the nine sets of duplicates considered here 

 yields the following results : 



Of these sets five are female, and four (including the two boys from 

 a set of triplets) male. The physical resemblance seems in all cases 

 to be complete, although I can corroborate this from personal inspection 

 in but three of the cases. The total difference in the palmar formulge, 

 excepting two cases in which the carpal areas are in question, consist 

 of but five instances, all of the left hand, and all of the slight nature 

 explained above. Since each palmar formula plus the character of the 

 carpus consists of 10 symbols, there are in all 90 sets of such symbols 

 in the above list, and if we deduct from these the nine which do not 

 correspond (two of the differences involve two symbols each) we find 

 an exact correspondence of 81 out of the 90 sets or 90 per cent of the 

 whole. To these formulas may be added, as they occur, 14 instances 

 of other features, such as patterns and lower triradii, 12 of which show 

 a complete and one a partial correspondence, while one alone, the small 

 hypothenar loop in No. V y, is unrepresented in its duplicate. 



