444 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



production on account of its increased opportunity of 

 variation, it has replaced the more primitive method 

 by the process of natural selection. 



The time when the impressions of physical habits 

 are conveyed to the reproductive elements has an im- 

 portant bearing on the question of inheritance. Pro- 

 fessor Osborn l has thus classified the agencies which 

 lie at the basis of organic evolution. Opposite to each 

 he states the theories which have been proposed to 

 account for them : 



A. Onto genie Variations. 



a. Gonagenic, i. e., those aris- Theoretically connected with 



ing in the germ-cells, including pathological, nutritive chemico 



physical, nervous influences, in- 

 cluding the doubtful phenomena 

 of Xenia and Telegony. 



Theoretically connected with 

 influences named above, also 

 with the combination of diverse 

 ancestral characters, Amphi- 

 mixis of Weismann. 



"blastogenic " in part of Weis- 

 mann, the " primary variations" 

 of Emery. 



b. Gamogenic, i. e., those aris- 

 ing from maturation and fertili- 

 zation, including the "blasto- 

 genic" in part of Weismann, 

 and secondary or Weismannian 

 variations of Emery. 



c. Embryogenic, i.e., those oc- 

 curring during early cell-divi- 

 sion, including the blastogenic 

 and somatogenic of Weismann. 



d. Somatogenic, i.e., those oc- 

 curring during larval and later 

 development after the formation 

 of the germ-cells. 



B. Phylogenic Variations. 



Variations from types originating in any of the above stages 

 which become hereditary. 



Theoretically connected with 

 extensive anomalies due to ab- 

 normal segmentation, and other 

 causes observed in the mechan- 

 ical embryology of Roux, Wil- 

 son, Driesch, and others. 



Connected with reactions be- 

 tween the hereditary develop- 

 ment forces of the individual 

 and the environment. 



1 American Naturalist, 1895, p. 426: "On the Hereditary Mechanism and 

 the Search for Unknown Factors of Evolution " 



