THE DETERMINATION OF DOMINANCE. 289 



Among the Neo-Mendelians the assumption is universal that 

 all the differences that come out of crosses are entirely due to 

 internal factors brought into the fertilized egg by the gametes 

 as factors and determiners, to various combinations of allelo- 

 morphs, and so on. That some of these variable conditions 

 may be due to external causes does not seem to have occurred 

 to any of the Mendelians, and no effort has been made to elimi- 

 nate in any one case what would first be eliminated in any ac- 

 curate physical or chemical work, namely, the effect of surround- 

 ing conditions, and forces incident upon the reactions unquestion- 

 ably going on in the developing individual. 



Probably most of us will admit that the fertilization process 

 represents the bringing together of two more or less like physico- 

 chemical masses, and the combining of these into a new body 

 with potentialities and capacities which then enable it to go on 

 in a constantly increasing series of epigenetic reactions, and onto- 

 genetic processes, and finally to evolve into an adult organism. 

 The essence of the activity and reaction involved are beyond any 

 question physico-chemical in their nature. This being true, the 

 first step in the elucidation of this complex array of variability 

 in behavior is to determine to what extent surrounding or inci- 

 dent forces may modify in a particular case the type of alternative 

 inheritance which is found ; when effects of these forces are known, 

 then attack can be profitably made upon problems of internal 

 factors. This first step I have in part accomplished in a series 

 of experiments which form the basis of this preliminary paper. 



Material. — The material upon which this series of experiments 

 herein described was carried out consisted of three species of 

 chrysomelid beetles of the genus Leptinotarsa, which would hybri- 

 dize freely and perfectly in all directions : Leptinotarsa signaticollis 

 Stal, a species occurring in southern Mexico at the foot of the 

 escarpment on the western side of the Mexican plateau ; Leptino- 

 tarsa undecimlineata Stal, a species confined entirely to the sa- 

 vannahs and lower foot hills from Tampico in Mexico, southward 

 to Costa Rica and Panama; and Leptinotarsa diversa n. sp., which 

 is very similar to the former but is limited entirely to the higher 

 foot hills on the border of the Mexican plateau. The reason for 



