EVIDENCES FROM CLASSIFICATION 99 



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-precipitation tests." This evi- 

 dence, as presented by Professor Scott, forms the substance of the next 

 chapter. 



