8 MODES OF RESEARCH IN GENETICS 



tinguished different orders or degrees of the soma- 

 togenic specificity of the germinal substance. 

 This fact has led to a good deal of confusion in 

 the use of the term "heredity." For example, 

 it is no doubt entirely correct to say that birds 

 have feathers because this sort of dermal covering 

 is hereditary in the class of animals specified. 

 But heredity in this sense means, both theoreti- 

 cally and practically, a very different thing than 

 when the equally true statement is made that a 

 Barred Plymouth Rock female inherits the barred 

 color pattern of her feathers from her sire only, 

 and not at all from her dam. In the first case 

 one is dealing with a phyletic matter, in the other 

 case with a sub- varietal. It is obvious that the 

 degrees of germinal specificity which determine 

 the two sorts of hereditary phenomena indicated 

 in the example must be of widely different orders. 

 One represents the substratal or general element 

 of heredity, the other the more superficial or 

 individualistic element. It is obvious that the 

 number of distinguishably different orders of 

 germinal specificity is as great as the number of 

 distinguishably different orders of variability, 

 which in turn is more or less closely reflected in 

 the various subdivisions or stages in taxonomic 

 classification. For practical purposes of thinking 

 and experimentation, however, it is sufficient to 

 distinguish two orders of germinal specificity ; 

 namely, a general and a special. It would be im- 



