102 Proceedings of the Royal Society of Edinburgh. [Sess. 
were not taken. These females, soon after emerging, began to reproduce 
on their birth plant. 
It is worth remarking that apterous females of M. ribis were trans- 
ferred to Gaieopsis, for this disposes of the view sometimes held that only 
certain forms are morphologically or physiologically suited to live on the 
second host plant, and that the winged migrants leave the first host 
because they are unfitted to feed there. Last summer I proved that the 
apterous females of Rhopalosiphum caprece, Fab. can live equally well upon 
Salix or Umbelliferse. Mordwilko (20) showed that Aphis sambuci, Linn., 
from the elder tree, could live and reproduce upon Lychnis, and I have 
repeated his experiment, using the apterous forms with complete success. 
It is the more remarkable that attempts to transfer M. ribis back 
from Labiatae to currant invariably failed, although no structural difference 
beyond an increase in size could be detected between forms reared on the 
two plants. A similar and even more striking case is that of Aphis 
grossularice, Kalt. ( = viburni , Scbrank). Here, after the first generation 
from the migrants, it is impossible artificially to establish the currant 
form back on the parent viburnum, although the viburnum form can, 
with some difficulty, be cultivated on the currant. Meanwhile two stocks, 
both founded by natural migrants from viburnum, breed throughout the 
summer on currant and viburnum respectively, and are structurally 
indistinguishable.* 
Table I. 
Control lines of descent showing per cent, of winged forms in each generation. 
Generation. 
Parent. 
Per cent, of 
Winged 
Forms. 
Generation. 
Parent. 
Per cent, of 
Winged 
Forms. 
A. II, 2 . 
Youngest 
40 
B. 11, 2 . 
Eldest 
74 
A. II, 3 . 
Eldest 
33 
B II, 3 . 
Youngest 
11 
1 A. II, 4 . 
Youngest 
16 
B. II, 4 . 
Eldest 
52 
A. II, 5 . 
Eldest 
17 
B. II, 5 . 
Youngest 
0 
■ A. II, 6 . 
Youngest 
7 
B. II, 6 . 
Eldest 
0 
A. II, 7 . 
Eldest 
0 
B. II, 7 . 
Eldest 
0 
A. Ill, 2 
Youngest 
51 
B. Ill, 2 
Youngest 
27 
A. Ill, 3 
Eldest 
48 
B. Ill, 3 
Eldest 
27 
A. Ill, 4 
Youngest 
29 
B. Ill, 4 
Youngest 
7 
A. Ill, 5 
Eldest 
7 
B. Ill, 5 
Eldest 
38 
A. Ill, 6 
Youngest 
9 
B. Ill, 6 
Youngest 
0 
A. Ill, 7 
Eldest 
0 
B. Ill, 7 
Eldest 
O' 
* Since the above went to press, I have found young fundatrices of Aphis grossularise 
on red currant. It is possible, therefore, that this species may undergo a complete cycle 
on Ribes. 
