PARTHENOGENETIC PURE LINE OF APHIS AVENGE FAB. IOI 



regard to variations in a parthenogenetic pure line is the great 

 predominance and great range of fluctuating, or individual, 

 variations; including under this head the variations in parts 

 of the body as well as variations affecting the whole of it. These 

 are the omnipresent, the conspicuous, and, I am tempted to state, 

 the characteristic variations in a parthenogenetic pure line. 

 It is true that we occasionally find an abrupt, or spontaneous 

 variation, but such variations are rare, and as a rule are in the 

 nature of omissions of parts or the arrest of the development of 

 the whole or a part of the individual. Fluctuating variability 

 has been shown by several workers to be greater where amphi- 

 mixis does not take place. Walton 1 has shown this conclusively 

 for Spirogyra. Hence, we may assume in the pure line of Aphis 

 avence here considered that the absence of amphimixis is a funda- 

 mental reason for the great range in fluctuating variability. 



FIG. 12. Camera lucida drawings, all of the same magnification, showing ex- 

 tremes of fluctuating variation in the lengths of the right antennae of three indi- 

 viduals (7311, 7312, and 7317) of the 731 fraternity. The heavy black line in each 

 case represents the body length, same magnification, of the individual whose 

 antenna is diawn by the side of it. 



The range of fluctuating variability is frequently so great 

 among the individuals of a single fraternity as to be quite notice- 

 able to the eye without measurements being made. In Fig. 12 

 we have camera lucida drawings, all of the same magnification of 

 the right antennae of three individuals of the ~ 3 i fraternity. Also 



1 Walton, L. B., 1915, "Variability and Amphimixis," Amer. Nat., Vol. XLIX., 

 pp. 649-687. 



