GALLS INDUCED BY PLANT-LICE 
81 
needles, and here undergo the fourth and last moult, casting 
off the pupal skin, which is left attached to the needles. 
The winged insects, or Alatae, are all non-migratory females 
They are yellow, with black head and upper thorax, and 
always have the third joint of the antennae distinctly shorter 
than the fourth, an important point in diagnosis. These 
winged females lay their eggs at the base of the buds, and 
die. From these eggs arise the Fundatriccs, and the life- 
history as above set forth begins anew. Particulars as 
regards the length of time the production of unisexual 
generations may continue are wanting; there is evidence, 
however, that it may extend over four years. At one time 
it was thought there was no male, but Blochmann and others 
have shown that this idea was erroneous. 
More than twenty years have elapsed since Blochmann 
announced the existence of a sexual generation in Chermes. 
Subsequently, Blochmann, Dreyfus, and Cholodkovsky, dis¬ 
covered, independently, the periodic migration of one 
generation from the Spruce to the Larch, and the return 
of a later generation the following year to the Spruce. 
Later, Cholodkovsky discovered the phenomenon known as 
“parallel series” in connexion with the generation on the 
larch. It has been investigated chiefly in this country by 
Burdon. His valuable paper,* entitled “ Some Critical 
Observations on the European Species of the Genus 
Chermes,” is indispensable to all workers in this difficult 
genus, as it contains tables of the results of Cholodkovsky’s 
investigations. 
Even the casual observer of the “ Pineapple ” galls on 
the Spruce cannot fail to note that they present marked 
differences in size and colour, and that some open much 
earlier than others. The largest of these galls is attributed 
to Ch. viridis , a species which is the “double ” of Ch. abietis ; 
it was formerly regarded as a variety of it. The Fundatrices 
and the Alatae differ from those of Ch. abietis in the darker 
colour (some shade of green) and the green eggs. The 
* Journ. Econ. Biol., 1908, vol. ii., No. 4. 
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