182 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
being dominant. The mutation can be traced back to a single indi- 
vidual — a heterozygous grass -green great-grandparent. The Mendelian 
factor for blue-green existed unsuspected in the true-breeding wild 
stock, but was brought to light by inbreeding. The offspring of two 
recessives (blue-green) bred true. The mutation is not sex-limited. 
Two non-inherited pigments — xanthophyll and chorophyll — derived 
from the food-plant form the basis of the dominant and recessive colours. 
Both probably exist together in normal grass-green hsemolymph. 
The hereditary nuclear enzyme, or recessive gene, involved in this case 
is a decolorizer (inhibitor) of xanthophyll. Since it is recessive it must 
be present in double dose (homozygous condition) in order to produce 
its effect. The wing-colour of the adult is not affected, but the eye- 
colour is — probably through some action of the blood. The egg and 
the pupal cuticula are also affected indirectly like the eye, and the 
blood also affects the colour of the cocoons spun by Hymenopterous 
parasites (. Apanteles flaviconchw ) emerging from the blue-green cater- 
pillar, for the silk is white instead of golden-yellow. The blue-green 
mutants are as vigorous and disease-resistant as the grass-green types ; 
but the adults are less active and less inclined to mate. The blue-green 
caterpillars are eliminated by sparrows ; the grass-green types are 
protected. J. A. T. 
Factors in Appearance of Winged and Sexual Aphides.— J. 
Davidson ( Sci . Proc. R. Dublin Soc., 1921, 16 , 304-22). The early 
aphidologists considered that food and temperature were the important 
factors influencing the apterous and winged forms in Aphides. From 
cytologica] investigations and recent breeding experiments it appears 
highly probable that the sequence of winged and apterous forms is 
largely due to some internal inherent tendency. Winged viviparous 
females tend to produce apterous viviparous females, and apterous 
viviparous females tend to produce either apterous viviparous females or 
a mixed progeny, including a very variable percentage of winged forms. • 
The apterous condition is to be regarded as an adaptation to seasonal 
food and temperature conditions. Similarly, food and temperature 
were regarded as the important factors affecting the development of 
sexual forms. But later cytological investigations show 7 that the 
appearance of the sexual forms is associated with changes in the 
chromosome complex. The agamic generations appear to be inter- 
polated between the winter egg and the sexual generation as adaptations 
to seasonal conditions. The approach of winter conditions would 
normally be the factor affecting the bringing to an end of the parthe- 
nogenetic phase and the appearance of the sexual forms. In some 
cases the production of the sexual forms may be superseded by continued 
parthenogenetic reproduction, certain agamic forms either reproducing 
slowly throughout a mild winter, or lying dormant and continuing 
reproduction the following season. In isolated cases, certain agamic 
individuals may be affected physiologically by some factor or factors, so 
that they do not respond to the inherent stimulus to develop into 
sexual forms. These individuals would normally die in winter, but 
under favourable conditions they may continue agamic reproduction. 
J. A. T. 
