112 H. E. EWING. 



8. Where selections were made in opposite directions (plus 

 and minus) in two isolations, each being used as a check against 

 the other, it was found that the fluctuations were simultaneous 

 in both isolations, and in the same directions, being thus inde- 

 pendent of the effects of selection. 



In Regard to General Biology. 



9. Fluctuating, or individual variations, are of great magnitude, 

 even in a single fraternity of a pure line of Aphis avence Fab., and 

 are frequently different on the two sides of the same individual. 



10. Abrupt, or discontinuous variations are very rare in a pure 

 line of Aphis avence Fab., and the few that were observed were 

 not proved to be inherited. 



11. The variations in stature, or body length in Aphis avence 

 Fab. are due largely to variations in temperature and food. 



12. The optimum temperature for the production of wingless 

 agamic forms in Aphis avence Fab. is about 65 F., and the 

 percentage of winged forms produced increases in accord with 

 the degree of divergence both above and below this optimum. 



13. Only wingless agamic forms are produced at a mean aver- 

 age daily temperature of about 65 F. 



14. A constant temperature of 90 F. is sufficient to prevent 

 completely the development of Aphis avence Fab. 



15. Long-continued parthenogenetic reproduction did not 

 affect the size, color, or fecundity of the strain of Aphis avence 

 Fab. used. The period of growth was somewhat shortened. 

 This may have been an adaptation, or response of the strain to 

 the artificial, suboptimum and almost constant conditions under 

 which they were kept. 



1 6. Psedogenesis occasionally occurs in Aphis avence Fab., both 

 among the nymphs of the winged form and nymphs of the wing- 

 less form. It is due to the arrested development of the body 

 in general, while the reproductive organs become completely 

 functional. All offspring of these psedogenetic nymphs that 

 grew to become adults were normal. 



17. Fluctuating variations are the omnipresent, the conspic- 

 uous, and in fact the characteristic variations in a pure line of 

 plant lice, and, as have before stated, they were not shown to 

 be inherited. 



