THE FOUR INSEPARABLE FACTORS OF EVOLUTION. 289 



6. These powers, as we have seen, under heredity are themselves partly 

 hereditary and transmissible; that is, individuals partly through heredity differ 

 in their powers of plasticity toward one or more new conditions. 



7. Individual adaptation, or accommodation, represents in part the result of 

 different degrees of plasticity. 



8. It also remains to be determined positively whether new ontogenic 

 characters are not in certain degree handed down to the blastos as well as to the 

 soma. 



9. Generation after generation new ontogenic characters may be handed 

 down in the soma which have no counterparts in the blastos; they would never- 

 theless by naturalists be reckoned among specific or varietal characters. 



10. It remains to be determined in what true sense ontogeny may be a factor 

 of evolution, e. g., through " coincident " or " organic selection" even with the 

 exclusion of the transmission of new ontogenic (somatogenic) characters. 



11. Under ontogeny should be considered the influence on the soma of 

 segregation, geographical and habitudinal, of isolation. 



12. Under ontogeny should be considered also all the laws of growth, such 

 as abbreviation, acceleration, retardation, development, degeneration, per- 

 sistence or stability of parts. 



13. Ontogeny should also be considered in its discriminating, guiding, and 

 selecting action. 



14. We should also consider how far there is through retarded or imperfect 

 adjustment in heredity to new conditions of life (a) a continuous evolution of 

 the soma as quite distinct from the continuous evolution of the germ plasm and 

 how far (6) this is responsible for the disharmony, or dysteleology in the human 

 subject, for example. 



15. As regards adaptability, plasticity, modifiability, these are the essential 

 initiating conditions not only of modifying certain organs but of originating 

 certain organs, changes of function, etc. There is a difference of theory regarding 

 plasticity, whether it is inherent in all living matter or whether the power of 

 plastic adaptation to new conditions is not part of a revival of hereditary powers 

 which were previously exercised under somewhat similar conditions. Plasticity 

 in relation to selection raises the question as to the survival of the most plastic 

 and most readily modifiable organism, or the organism which is most readily 

 modifiable in the course of ontogeny. 



16. In experiment and investigation somations or modifications should be 

 considered under four aspects : 



(a) As affecting heredity primarily, in which the influences are less clear and 

 rapid. 



(6) As affecting ontogeny primarily, in which the influences are most clear and 

 rapid. 



(c) As affecting both heredity and ontogeny simultaneously. 



(d) As affecting ontogeny then heredity. 



19 JOURN. ACAD. NAT. SCI. PHILA.. VOL XV. 



