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THE QUARTERLY REVIEW OF BIOLOGY 



(19x6), asymmetry in eyes, ear-form, etc. 

 by v. Verschuer (19x7), and the occurrence 

 of naevi by Siemens (19x4b). 



The result is somewhat different accord- 

 ing to the characters considered. But 

 symmetry reversal is rather frequent 

 among identical twins for nearly all these 

 characters. This is especially the case 

 with handedness (Lauterbach, 19x5; 

 Dahlberg, 19x6; v. Verschuer, 19x7). 

 But the puzzling fact is that left-handed- 

 ness is decidedly more frequent among 

 fraternal twins as well as among identical 

 twins, than in the general population. 

 Left-handedness ought, therefore, to be 

 considered a phenomenon directly con- 

 nected somehow with twinning in a 

 general sense, and not necessarily with the 

 special kind of twinning bringing about 

 identical twins. 



Siemens' diagnosis of twins (19x4b, 

 19x7), which has since been used rather 

 extensively, is based on a good many 

 physical features, that is 



"A. Traits which agree in one-egg twins almost 

 always and almost completely; in two-egg twins only 

 rarely: 1. hair color and form, 2.. eye color, 3. skin 

 color, 4. downy hair of the body; B. traits which 

 agree in one-egg twins, and which usually vary more 

 widely among two-egg twins: 5. freckles (location 

 of), 6. appearance of blood in the skin (teleangiec- 

 tasis, cutis marmorata, acroasphyxia), 7. follicular 

 processes (lichen pilaris, acne), 8. tongue (furrowed 

 or not) and teeth; C. traits in which one-egg twins 

 usually, two-egg twins only rarely show strong 

 resemblances to each other: 9. form of face (physiog- 

 nomy), 10. form of ear, 11. form of hands (and of 

 nails), it. body build;" besides "13. mental make-up 

 (school standing, character, talent), 14. illness and 

 abnormalities, 15. traits which are the bases of special 

 methods of investigation (finger prints, microscopic 

 comparison of the capillaries, refraction of the eyes, 

 blood groups and so on" (Siemens, 192.7, pp. 2.05-2.07). 



There is no doubt that this scheme is 

 more comprehensive and naturally safer 

 than others hitherto proposed. It has, 

 however, a rather limited application to 

 twins among races in which the hair-color 



and form, eye color and skin color are 

 subject to only a slight variation as, for 

 instance, the Mongolian race. 



Dahlberg (19x7), lastly, puts emphasis 

 on the usefulness of the ear form for this 

 purpose. 



FINGER, PALM AND SOLE PRINTS 



Galton (189X) was the first to recognize 

 the close similarity existing between the 

 friction-ridge patterns of fingers of some 

 same-sex twins. He compared the prints 

 of fore, middle, and ring fingers of the 

 right hand of 34 pairs of twins, and found 

 that in some of the pairs the agreement of 

 the patterns was so close that they should 

 be assigned to the same class according to 

 his classifying scheme, while in others the 

 correspondence was only partial and in 

 still others no correspondence was found. 



Wilder (1904, 1908, 1919) worked on 

 some 50 sets of palm and sole prints of 

 twins, besides 16 sets of finger prints, and 

 came to the conclusion that 



"the friction-skin configuration of twins corroborates 

 the conclusions based upon the general physical 

 appearance, that there are two distinct types of 

 human twins, duplicate (or identical) and fraternal." 

 "The correspondence in the friction-skin configura- 

 tion is confined to the general plan of the surface as a 

 whole and does not extend in the least to finer details, 

 the 'minutiae' of Galton.' ' "In duplicate twins there 

 is, in both hands and feet, a marked correspondence 

 between the two sides, so that the right and left hands 

 of each twin correspond as completely as do the right 

 or the left hands of the two individuals. All four of 

 the hands involved are thus duplicates of virtually 

 the same picture, and the same phenomenon is shown 

 in the four feet" (1919, p. 2.). 



Poll (1914) studied finger prints of 83 

 pairs of presumably identical twins be- 

 sides two sets of triplets and one pair of 

 pygopagus. In no case did he meet with a 

 correspondence of all fingers even as 

 regards the type of pattern. Rarely nine 

 fingers were similar and one different. 



Ganther and Rominger (19x3) worked 



