442 Duplicate Twins and Double Monsters 



but in No. II the reversed pattern is a tented arch to which a small 

 loop is applied laterally, being nlnar and radial respectively in the two 

 individuals. As for the side upon which it occurS;, it is right in two 

 cases and left in two. In seeking for an explanation, the theory of the 

 transposition of viscera in twins is recalled to mind, and especially 

 Bateson's statement that the transposition need not necessarily be a com- 

 plete one, but why the tranposition should affect one finger alone, or 

 why that finger should always be the index, these are at present questions 

 beyond solution. 



With the evidence thus far at hand, the impression becomes strong 

 that in typical duplicate twins, the following conditions of the friction- 

 skin configuration ought to co-exist with the correspondence in other 

 physical characters, and probably with that of a single placenta and 

 chorion during development, namely: (1) Duplicate formulae for the 

 main lines and for the carpus; and (2) Approximate correspondence 

 in other features such as lower triradii, seams, and jjatterns; to these 

 may be added as usual, though not necessary, (3) Bilateral symmetry 

 between the hands of the two sides, and (4) A reversal of the patterns 

 of one of the indices, either right or left. 



DETAIL OF ACTUAL PALM PRINTS OP DUPLICATE TWINS. 



For the purpose of enabling the reader to study actual conditions, I 

 have reproduced in Fig. 7, the prints of the left hands of No. I, the 

 tracings of which have been already published (in Amer. Jour. Anat., 

 Vol. I, p. 438). These are good typical duplicates, and although as 

 subjects they may not be as good as those possessing more patterns and 

 other details, they were the only subjects from which I was able to pro- 

 cure prints satisfactory enough to be used for this purpose. 



In these the four main lines are identical in their general course and 

 in their effect in the formation of areas, but differ slightly in the relative 

 proportions of the areas they demark. It is as tliougli identical forces 

 had directed the development in the two individuals, hut that the mate- 

 rial had yielded a little unequally to the strain of growth, a givm area 

 being a little more expanded and consequently covered Tjy a feiv more 

 ridges in one than in the other. The result is a slight variation in the 

 curvature of the main lines and in the number of ridges between them 

 *' at identical spots in the two individuals. Line A, arising from the 

 triradius at the base of the index finger, curves around the base of the 



Fig. 7. Prints of the left palms of Twins No. 1. Natural size. The lines of 

 interpretation are marked with India ink. (Figure on opposite page.) 



