GALLS INDUCED BY PLANT-LICE 83 
gall is a small pale green thing, about the size of a pea, with 
a whitish, waxy bloom (Fig. 2). It ripens very early, and 
usually opens in the middle of June. The Alatae migrate 
to the Larch, and deposit their eggs on the needles. The 
resulting Colonici hibernate on the bark of the branches, 
and deposit numerous greenish-brown eggs at the base of 
the buds in spring. Fig. 3 shows a third-year Larch shoot 
at the end of March, with Colonici and their eggs, and Fig. 4 
presents an enlarged view of one with its eggs; there is no 
wool. The generation which hatches from these eggs in 
May and June departs from the sequence observed in the 
life-cycle of Ch. viridis, and, instead of winged Sexuparae only, 
which migrate to the Spruce, we find that the generation 
usually splits into two parallel series—wingless insects known 
as Exules and the winged Sexuparae. The larval stages of 
both are spent on the Larch needles, which often bend at 
right angles at the point attacked. Figs. 5 and 6 show 
eggs of Exules and Sexuparae on bent Larch needles. The 
afflicted needles are often slightly swollen at the affected 
part (Fig. 5), and become yellow. The winged sexuparae 
(Figs. 9, 10) fly back to the Spruce and deposit their eggs 
on the needles. Fig. 7 depicts a Larch shoot with Colonici, 
Exules, and winged Sexuparae, some of the latter starting 
on their migration to the Spruce. The eggs are said to vary 
in colour according to the sex, the yellowish-green ones pro¬ 
ducing male, the reddish ones female, sexuales. The female 
deposits her single egg on the shoot, and this egg yields the 
Fundatrix. The wingless Exules remain on the Larch, and 
lay greenish-brown eggs on the needles. There may be two 
generations during the summer. Fig. 8 shows an Exule 
with its pupal skin on a Larch needle. With the approach 
of winter they withdraw to the branches to hibernate, and 
are then identical with the Colonici. 
The double of Ch. strobilobius Kalt. is Ch. lapponicus Cholod., 
which in its life-cycle resembles Ch. abieiis. The Fundatrices 
are seated on the bud, never below it, and differ from those 
of Ch. strobilobius in the larger size, more copious excretion of 
