96 Proceedings of the Boyal Society of Edinburgh. [Sess. 
Stachys sylvatica . . . Kaltenbach and Buckton. 
Polygonum persicaria . . Buckton. 
„ hydropiper . Kaltenbach. 
„ laxiflorum . „ 
„ lapathifolium . . „ 
With regard to the distribution of the sensoria on Joint V, out of forty - 
one specimens collected in the field on June 25th, thirteen had the red blister 
and twenty-eight the green leaf type. From this it may be inferred that 
both forms are migratory from the currant, for the early date precludes the 
idea that they could have been established on the Galeopsis long enough 
for the change of host to have affected the antennal development. I was 
not able to determine whether the type remained constant through several 
generations on Galeopsis, because in the laboratory this stock produced a 
few apterous generations only and then died out. The green leaf form 
introduced from currant produced only the green leaf type of Joint V, 
though in the first generation on Galeopsis, nine examples out of thirty- 
eight had a number of small sensoria all over the shaft of the joint, but 
this did not appear in the later generations. 
I made several attempts to transfer different generations of this stock 
back to currant, but they were invariably unsuccessful, as the following 
extracts from my notes show : — 
July 18. Transferred two winged and five wingless females (second 
generation on Galeopsis) back to currant. 
July 19. Feeding and produced two young. 
July 21. All dead but two wingless forms which have lost their green 
translucent colour and become yellow and opaque. 
July 25. Both females dead. 
Later experiments always failed, and the aphides died in a few days 
without reproducing. Even in autumn, when it might have been supposed 
that a return migration to currant would take place, neither winged nor 
wingless forms re-established themselves, but crawled about the cage until 
they died of exhaustion. This inability to live on the first host after 
transference to the second is curious. At first I thought it might be 
explained by a structural change, such as is suggested by Kaltenbach’s 
statement of a shortened rostrum in galeopsidis as compared with ribis, 
but on examination both of these, and of transferred forms, I can find no 
difference at all. 
