92 H. E. EWING. 



genetically for more than half a hundred generations, but in 

 such cases, I believe, no checks have been made to see if de- 

 terioration of the stock was taking place. 



After breeding Aphis aventz Fab. for 73 generations partheno- 

 genetically, I found the species breeding at Ames, la., on oats 

 and barley that was being raised for experimental purposes. I 

 decided to start a check strain with these Iowa forms to see if 



FIG. ii. Plot showing results obtained by running the Iowa strain of Aphis, 

 avence Fab. as a check on the Oregon strain to show the effects of long-continued 

 parthenogenetic reproduction. The solid lines are for the fluctuations in the 

 Oregon strain, the others for the Iowa strain. Plan of curves the same as in Figs 

 7, 8, and 9. 



the continued parthenogenetic reproduction had reduced the 

 virility of the experimental line obtained from a wild agamic 

 female in Oregon. 



A careful comparison of the Iowa forms with those of the 

 seventy-third generation in my pure line showed no structural 

 differences. They were somewhat different in coloration, being 

 a deep, dark green, while those being used in the experiment were 

 a light yellowish green. The cinnamon areas about the bases 

 of the cornicles were well marked, but apparently were not so 



