1918-19.] Life-History and Bionomics of Myzus ribis, Linn. 97 
Table G. 
Dimensions of alate female of Myzus ribis. First generation on Galeopsis tetrahit. 
Absolute 
Dimensions. 
Dimensions ex- 
pressed as per 
cent, of Length 
of Forewing. 
Length of forewing ..... 
mm. 
3T3 
per cent. 
100 
Length of body ..... 
2-26 
7 
Breadth across abdomen .... 
•72 
23 
Breadth between cornicles . . . j 
•30 
9 
Total length of antenna . . . . ! 
2*80 
89 
Length of cornicles | 
•20 
6 
Table H. 
Average dimensions of twelve alate females of Myzus ribis. First generation 
on Galeopsis tetrahit. 
Average Absolute 
Dimensions. 
Dimensions ex- 
pressed as per 
cent, of Length 
of Fore wing. 
mm. 
per cent. 
Length of forewing ..... 
343 
100 
Total length of antenna .... 
2-91 
84 
Length of cornicles ..... 
•25 
7 
The Generation Series. 
The generations descended from two stem mothers, A and B, were 
followed throughout the summer. Four lines of descent were chosen from 
each stock : — 
A (B) 1= eldest-born of eldest-born. 
A (B) 11= | eldest- and youngest-born chosen alternately from 
A (B) 111= j each generation. 
A (B) IV = youngest-born of youngest-born. 
The second and third lines were intended only as controls in case it should 
prove desirable to obtain a mean between the eldest and youngest series. 
These observations were made on aphides kept in the laboratory. I 
intended to have identical series, founded from the laboratory stock, 
“ sleeved ” on currant bushes in the garden under entirely natural condi- 
tions ; but in wet, windy weather it was found impossible to make accurate 
records each day of the number of young, etc. Details were therefore 
discontinued, but the garden series were maintained as controls for the 
VOL. xxxix. 7 
