a 
PAPERS ON ZOOLOGY AND PHYSIOLOGY 31 
G4 00 Ea Fe | 
Fig. 1. GRAPH SHOWING REGRESSION IN SUBLINES OF A PURE LINE OP 
THE PARTHENOGENETIC PLANT LOUSE (Aphis avenae Fab.). PARENTS ARE 
ARRANGED INTO GROUPS REPRESENTING VARIATIONS IN LENGTHS OF 0.05 MM. 
THESE PARENTAL GROUPS OR CLASSES ARE REPRESENTED IN FIGURE BY CIRCLES 
SHOWING THEIR RESPECTIVE LENGTHS. THE MEAN LENGTH OF ALL THE OFF- 
SPRING OF PARENTS BELONG|NG TO EACH GROUP ARE REPRESENTED BY ARROW- 
HEADS. AMOUNT OF REGRESSION IS IN EACH INSTANCE INDICATED BY ARROW, 
THE BROKEN LINE JUST BELOW 1.55 REPRESENTS THE MEAN OF THE LINE, 
THE HEAVY CIRCLE IS FOR THE POSITION OF THE MEANS OF ALL THE PARENTS 
ABOVE THE MEAN OF THE LINE, AND THE HEAVY ARROW FOR THE REGRESSION 
OF THEIR OFFSPRING. 
This mean is only 0.011 mm. above the mean of the line, 
hence regression, thus measured is found to be practically com- 
plete (see heavy arrow in Figure 1). Since so few parent in- 
dividuals are below the mean, we will have to regard their 
numbers as being insufficient for a test similar to those above 
the line. 
