90 
Proceedings of the Royal Society of Edinburgh. [Sess. 
thenogenetic line are not inherited ; but the number was small, and it was 
not shown whether the somatic variations recorded were adaptations to the 
special environment of the parent, or to a fixed characteristic of the strain 
employed. If the latter, the results were in accordance with the known 
rule that children of much varying parents tend to regress to the mean 
of the race. 
Myzus whitei, Theobald, and Myzus dispar, Patch. 
Two species closely resembling M. ribis, Linn., have been recorded 
from England and America respectively. 
Theobald (27, p. 110) describes M. whitei , taken in the winged form 
only, on black and red currants. He says that it might be mistaken for 
M. ribis, but it is darker, the three to seven sensoria occur only on the 
proximal half of Joint Y, the abdominal markings are distinctive, and the 
eyes are dark. A coloured plate of the two species is given, in which, how- 
ever, both are figured with the red eyes of M. ribis. It has been shown 
already that the sensoria on Joint Y are extremely variable, and therefore 
cannot alone be made the basis of a new species. As regards the abdominal 
markings, M. ribis is figured with three distinct transverse bands on 
segments 5-7, and four lateral spots on each side of segments 2-5, 
M. whitei is shown with a single large patch on segments 4-6, and two 
lateral spots on 2-3. Hitherto all the specimens that I have seen of 
M. ribis have had the square abdominal patch ascribed by Theobald to 
M. whitei. The lateral spots vary, but are generally three in number on 
segments 3-5, though some specimens have two (on 4-5) or four (on 2-5). 
I thought at first that the green leaf form might be identical with M. 
whitei ; but this explanation will not cover the discrepancy of the colour 
of the eyes and abdominal markings. Flogel (11) does not mention the 
abdominal pattern in the parthenogenetic female, but he figures the 
winged male with a single large spot, exactly similar to that of M. whitei. 
Kaltenbach (16) says that M. ribis has a square patch in the middle of 
the abdomen, and three or four smaller ones at the sides. Koch’s figure 
(19) resembles Theobald’s M. ribis in having three distinct regular bands, 
but in the text he says : “ On the back of the abdomen is a confluent 
black mark ( £ ein gemeinschaftlicher Fleck ’) on the 4th, 5th, and 6th 
segments ; and in addition, at the side of the four anterior segments, a 
small mark also black.” These descriptions apply better to the M. whitei 
than to the M. ribis of Theobald’s figures; and I am inclined to think 
that M. whitei may prove to be only a variety of M. ribis, especially as 
Patch (23) remarks that in some collections of the latter species the 
