EVIDENCES FROM CLASSIFICATION 123 
though the proof has not been forthcoming. Everyone is familiar 
with the remarkable similarity, amounting almost to identity, between 
such twins. Thus we are able to show that the closest blood relation- 
ship known is associated with the closest resemblance. The next 
degree of resemblance is between members of the same family, 
brothers, sisters, cousins, etc., and we do not hesitate to explain this 
resemblance as due to blood relationship. In this we merely accept 
the known principles of heredity. 
The second direct test of the validity of the assumption that 
degrees of resemblance run parallel with degrees of blood relationship 
is found in connection with “blood-transfusion tests.”” This evidence, 
as presented by Professor Scott, forms the substance of the next 
chapter.—Ep.] 
