182 Annual Report for 1905 of the Zoologist. 
It is necessary at the outset to state one remarkable 
«/ 
characteristic of the aphis tribe, namely, that they are able to 
produce young for many successive generations by females 
only, without the intervention of anv male. After several 
such generations a brood ordinarily appears comprising both 
males and females, and the eggs which result from their 
pairing hatch out into females only, which begin a new 
succession of broods containing no males. This may all 
happen on the same plant, or the insects may migrate from 
one plant to another, in which case the sexual generation is 
generally confined to one plant, though the purely female 
broods may occur on either. 
It has long been known that the cone-like galls or “ false 
cones ” often found on spruce trees were the work of an insect 
of this group, which has been named Chermes cibietis. We 
have also, for a long time past, been acquainted with a Chermes 
attacking the needles and twigs of young larches, and the 
trunks of older trees, and showing its presence by exuding a 
white woollv substance, and this has been described as Chermes 
laricis. Some years ago the researches of several investigators, 
— notablv Drevfus and Blochmann — led to the belief that these 
two apparently distinct creatures were in reality one and the 
same, the sexual generation only occurring on the spruce, but 
some of the winged females migrating to the larch and, with 
changed habits and slightly changed appearance, producing 
several purely female broods before returning to the spruce 
for another sexual generation. 
If this view is correct, it has obviously a very important 
bearing on practical forestry, for it condemns the practice of 
intermingling spruces and larches, and it indicates, moreover, 
that the entire absence of spruces would put an end to the 
disease on the larches, unless the insect can propagate itself 
indefinitelv bv females only. 
Among more recent investigations those of the Russian 
zoologist, Cholodkovsky, are, perhaps, the most important, and 
the following are among the conclusions at which he arrives. 
He finds that the spruce galls may be inhabited by various 
kinds of Chermes, two of which specially concern us. 
One, which he identifies as Kaltenbach's Ch. abietis , has 
the hibernating female yellow, long, and narrow, the winged 
form bright yellow, with the fourth joint of the antennae longer 
than the third, and laying yellow eggs, which hatch into 
larvae with long suckers. The other, which he identifies with 
Ratzeberg's Ch. viridis , has the hibernating female green, 
and broad-oval, the winged form reddish, with the third joint 
of the antennae longer than the fourth, and laying green eggs, 
which hatch into larvae with short suckers. 
