Vol. XXX. March, igi6. No. j 



BIOLOGICAL BULLETIN 



PALM AND SOLE STUDIES. 



HARRIS HAWTHORNE WILDER. 



(Continued from page 172.) 



V. FRICTION-SKIN CORRESPONDENCE IN PYGOPAGI. 



A long series of studies of the palm and sole markings in human 

 twins, both duplicate and fraternal, 1 has established two principles 

 for twins of the true duplicate type (monochorial, monosexual, 

 striking facial resemblance, etc.), viz: (i) that the corresponding 

 palms and soles in the two individuals are strikingly alike in 

 friction-ridge configuration, even duplicating singular and unusual 

 features, and (2) that the correspondence in the two sides of the 

 same individual is far greater than is usually the case, so that the 

 four hands involved, or the four feet, present so many copies of 

 practically one picture. To these may be added a third condition, 

 not absolutely constant, but frequently noted; a reversal of the 

 pattern of the index figures in the two individuals, affecting either 

 the two right hands or the two left hands, or occasionally both 

 sets. 



In this connection it is a matter of great importance to ascer- 

 tain the condition of the friction ridges in "conjoined" twins, that 

 is, in twins which have never completely separated, but remain 

 throughout life united by certain common parts (i. e., double 

 monsters). The numerous specimens of this sort found in 

 teratological museums have yielded some results, which seem to 

 accord with the findings in separate duplicate twins, but such 

 objects are unsatisfactory to study since they are mostly embry- 

 onic, or newborn, and the ridges in consequence are very soft 

 and indistinct, while the fluid in which they are preserved renders 

 a print difficult or impossible. 



Recently, however, I have had the opportunity of making 



1 Wilder, 1902. 1904, 1911. 



211 



