Modification of Germinal Constitution of Organisms 167 



violets or plants, but is coming to be recognized as common 

 in nature. 



The production of germinal variations occurs by combin- 

 ing slightly different conditions of the same attribute in the 

 zygote (fertilized egg) . This process, amphimixis, commonly 

 advanced by neo-Darwinians, has at present almost no evi- 

 dence in support of the theory that departures beyond the 

 normal range of variation can be produced thereby, but it 

 is at least a conceivable method by which variations might 

 well arise, and is open to direct experimental investigation. 



The origin and development of variations through the 

 operation of orthogenesis, a name descriptive of a condition, 

 but personified to represent the agencies productive of the 

 condition observed. It is conceivable that changes started 

 in one direction or another may continue in that direction 

 on the basis of the operation of the law of inertia, in a 

 uniform direction and at a uniform velocity until they reach 

 limits imposed by the physical nature of the part or of the 

 organism in which they arise, or until they reach a stage of 

 development where they become of selective value, and may 

 be accelerated, retarded, or turned in other directions. 



In all of these possible modes of origin of germinal 

 variations two groups of factors are always involved: first, 

 the physical constitution of the material, with its array of 

 qualities, attributes, and conditions, which is always the 

 genetic product of an immense series of antecedent stages; 

 second, incident forces from without the germinal material. 

 These two groups of factors sustain definite and fundamental 

 relations to each other, and the effort to understand the 

 relations between these two fundamental groups has 

 stimulated much of the investigation of the last decade. 

 The physical or gametic constitution is the constant, and 



