THE UNKNOWN FACTORS OF EVOLUTION. 93 



than we have hitherto suspected. Thus a vast amount of 

 evidence which has been brought forward as proof of Buff on' s 

 factor, i.e., of the direct action of environment in producing 

 definite and adaptive ontogenic variations is in reality in many 

 cases no proof at all. 



Having thus eliminated errors of interpretation, the great 

 question still remains as to what happens when the environ- 

 ment is a wholly new one in the historical experience of the 

 organism. Do the ontogenic variations exhibit a new direc- 

 tion .'' Is this direction adaptive, i.e., towards progressive 

 adaptation } What relations have such new conditions to the 

 hereditary potencies of the germ-cells } 



Out of all actual researches it becomes clear that experi- 

 mentation can henceforth be separately directed upon the four 

 stages of development, and that it will be possible in some 

 degree to draw such lines of separation. New mechanical and 

 chemical influences can be applied in each stage and withdrawn 

 in the subsequent stages, the difficulty being to reach the 

 extreme point where a profound influence is exerted without 

 interfering with the reproductive functions. 



One effect of new environment upon the gonagenic, gamo- 

 genic, and embryogenic stages will be saltation. Ryder ^ has 

 recently treated this in a most suggestive manner in discussing 

 the origin of Japanese gold-fish. Turning to St. Hilaire's hy- 

 pothesis, we find he had in mind embryogenic variation mainly 

 traceable to respiratory and chemical changes. Virchow ex- 

 tends the cause of sudden change further back to chemico- 

 physical influences upon the germ-cells. The causes and 

 modes of sudden development arising from whatever ontogenic 

 stage demand the most careful investigation, chiefly in their 

 bearing upon the relation of ontogenic to phylogenic variation. 

 Galton has discussed the subject objectively under the head 

 of ' Stability of Sports,' and Emery, under the head of ' Primary 

 Variations,' has supported Galton's observation that such salta- 



1 The inheritance of modifications due to disturbance of the early stages of 

 development, especially in the Japanese domesticated races of gold-carp. Proc. 

 Acad. Nat. Sc. Phila., 1893, p. 75. 



