HEMIHYPERTROPH Y 1 6 1 



is that given above, viz., that there was noted in one case 

 of right-handed hemihypertrophy a reversed asymmetry 

 of the epiglottis. 



An interesting discussion entitled "Twinning and 

 Asymmetry" in Dr. Gesell's paper appears to me to be 

 of sufficient interest to deserve quoting at some length: 



TWINNING AND ASYMMETRY 



It is natural that a discussion of the etiology of hemihyper- 

 trophy should finally bring us to problems of double psychical 

 personahty and twins. Further researches into the biology of 

 twinning may bring the remarkable phenomenon of unilateral 

 hypertrophy more completely within our comprehension; may 

 even prove it to be on closer scrutiny more frequent and less 

 anomalous than we had supposed. Indeed, even now, all things 

 considered, the real marvel is not the occurrence of hypertrophy 

 but the fact that hemihypertrophy is such an extreme rarity. 



By twinning we mean the production of equivalent structures 

 by division. This statement is taken from the biologist Bateson, 

 who regards the power to divide as a fundamental attribute of 

 life. The tendency to symmetry, to bilateral equivalence or 

 mirror-imaging is so general that it must be regarded as a funda- 

 mental of biologic mechanics. Hemihypertrophy accordingly may 

 be conceived as some profound inaccuracy in the natural process 

 of developmental dupHcity. It is not as monstrous as the double 

 monsters, but it may have a related morphogenesis. At any 

 rate, we can safely assume that hemihypertrophy is not an artifact 

 really consisting in a hemi-atrophy. It is evidently a mild 

 unilateral gigantism of an individual whose lesser somatic half is 

 normal. 



In a certain biologic sense we may regard every bilateral 

 individual as being a pair of twins. H. H. Newman, in his fascinat- 

 ing work on The Biology of Twins, holds that monozygotic twinning 

 — where a single egg produces two offspring — is "a phenomenon 

 that should be considered as only a phase of the much more general 

 phenomenon of symmetrical division. The development of the 



