HEMIHYPERTROPHY 1 63 



and perhaps also cases of human hemihy per trophy, as 

 due to a physical inequality of the two bilateral primordia 

 so that one side would be more affected by subnormal 

 conditions than the other. Even in cases of double 

 monsters there is often a pronounced difference in the 

 two components that is probably based upon some early 

 physiological inequality of the two bilateral primordia. 

 Even with this possible explanation of asymme- 

 try in mind I find myself in essential agreement with 

 Dr. Gesell in his interpretation of hemihypertrophy as a 

 minimal phase of double monstrosity. We may conclude 

 that, since twinning in general consists of a more or 

 less complete isolation, physiological at first and later 

 physical, of the bilateral primordia of a single embryonic 

 axis, there may readily occur shght degrees of physio- 

 logical isolation or independence of the two halves of the 

 body. Hemihypertrophy, complete and incomplete, 

 would then be the result of such relatively slight isolation 

 and would therefore logically belong in the same series 

 with duplicate twins, double monsters, and other types 

 of twins. The unilateral hypertrophy would be thought 

 of as the result of some deficiency confined to one side, 

 and the associated peculiarities would be viewed as 

 secondary consequences of the primary deficiency. 



