36 Miss Haviland, Preliminary Note on Antennal 



reason, in the population used in 1919, it was unusually low. It is 

 hoped to repeat and extend the range of the experiments in 1920. 

 The character chosen is the distance between the sensoria of 

 antennal segments v. and vi. and the articulation of these 

 two segments, expressed as the percentage of the width of the 

 head between the eyes. The ratios are shown separately for 

 each segment, with a dividing line to represent the articulation. 



^, ,„ , , ,, , Seg. VI. = 19% of the head- width 



Thus J# denotes that -^ ■^, — j— j — ^ — . ,^, . 



^ Seg. V. = 8% of the head- width 



Each generation is designated by combinations of two letters: 

 E, (= red leaves) and G (= green leaves) and numerals, which 

 express its complete ancestry. Thus ^^^^ denotes the fourth 

 generation from the fundatrix of the population, and the F^. 

 generation after transference to Green leaves after two consecutive 

 generations on Red blistered leaves. In the transferred generations, 

 the aphides were removed to the new environment when less than 

 twelve hours old. The individuals for transference were selected 

 wholly at haphazard. Thus, if a brood mother Eg gave birth to 

 four young in the day, two were transferred to red blistered leaves, 

 and two to green leaves, and so on in equal numbers from day to day. 



The pure Red (RRR, etc.) lines, and pure Green (GGG) lines 

 were used as controls. The latter unfortunately became extinct in 

 the third (Gg) generation. Hence for later generations the next 

 longest unbroken line on green leaves (R2G0, etc.) had perforce to 

 be taken as the control, though as it had been fed for the first two 

 generations upon red leaves, it cannot be regarded as wholly * 

 satisfactory. In Table 1, the curves of error of the ratios of genera- 

 tions R2, R4 and R2G4 are shown. Rg is the common ancestral 

 generation. The mode of the curve of R4 tends to shift to the left, 

 i.e. the ratios of the antennal segments to the head-width are 

 smaller. For the sake of clearness, in the graph only the curve of 

 R4 is shown, but those of Rg, R5 and Rg, though with a smaller 

 number of individuals, are almost identical with it. The curves of 

 the ratios of R2G1 and R2G2 are very similar to their red controls. 

 The R2G3 generation produced very few winged individuals, but 

 these indicate a somewhat greater range of variation in Seg. vi. 

 The curve of R2G4, as shown in the graph, has a marked tendency 

 to shift to the right, indicating that the ratio of the antennal 

 joints to head-width has increased, and this tendency is maintained 

 in the succeeding generations, R2G5 and R2Gg. The position in 

 the generation series does not account for the change in the 

 antennal structure, for the modes for the six Red generations are 

 nearly identical. 



So far we have considered only the modes. The mean ratios 

 of the different generations are dealt with in the succeeding tables. 



I 



