BLASTOGENIC VARIATIONS. 117 



seventeen years of age.* The following are the 

 measurements made: 



PER CENT. 

 TWIN A. TWIN B. DIFFERENCE. 



Stature, 172cm. 170cm. 1.2 



Left arm, 74 74 0.0 



Right arm 71 74 4.1 



Left upper arm, .... 27 27.5 1.8 



Forearm 27 26 3.8 



These slight differences are probably due to the effect 

 of external influences acting during the course of de- 

 velopment, or are somatic, as distinguished from blas- 

 togenic, variations. 



In a series of measurements on twin brothers 

 obtained by the author, the resemblance was very much 

 closer, the difference in no case reaching even 1 per cent. 

 These brothers, aged twenty-three, were extraordi- 

 narily alike in physiognomy, and, moreover, they 

 had both suffered at the same times from the same 

 diseases, viz., bronchitis, measles, chicken-pox, mumps, 

 and influenza. The slightly smaller one of the two 

 had had a rather more severe attack of bronchitis than 

 his brother, when a year and a half old, and so, perhaps, 

 but for this, the physical resemblance would have been 

 even closer: 



PER CENT. 

 TWIN A. TWIN B. DIFFERENCE. 



Standing height 173.00cm. 172.67cm. -.19 



Sitting height (from seat of chair), 88.03 87.87 .18 



Span of arms, .... 179.90 179.88 -.01 



Length of right mid-finger (from 



metacarpo-phalangeal joint), 10.99 10.98 .09 



Span of hand, .... 21.33 21.30 -.14 



Length of skull (occipital protuber- 

 ance to base of nose), . . 18.52 18.42 .54 



Maximum breadth of skull, . . 15.13 15.01 .80 

 f "Germ-plasm," p. 253. 



