DIMOEPHISM. 
91 
ones may be found in the ovisacs ready to supply the 
places of those which are ripe for extrusion. 
DIMORPHISM. 
An interesting subject connected with these insects 
is the tendency shown by some to take double forms. 
In a certain degree this even may be seen in the con- 
trast between the foundress or first parent (Altmiitter) 
and the individuals of the last brood, just before the 
process of oviposition commences. The early spring 
form of Chermes lands is different from that of all her 
progeny till the last, and the same remark applies also 
to A^phis mail and other species. These variations 
relate not only to size and colour, but also to consider- 
able change of form and modification of parts. Some 
such modifications in a smaller degree we find also in 
the queen wasps, ants, and bees, and markedly so in 
the Bomhidce which survive the winter. 
Perhaps the most remarkable example of Dimorphism 
amongst Aphides is to be found in GJiaitophorus aceris^ 
the early spring forms of which occasionally are so 
diverse that they have been described as belonging to 
not only different genera but distinct families. Thus Mr, 
Thornton, the original discoverer of this extraordinary 
insect, gave it the name of Fliyllojplioriis testuclinatiis ; 
afterwards Mr. Lane Clark styled it CJielymorjpha 
testudo and placed it between the Jjohididce and the 
CocddceA'^ 
Another striking example presents itself in the Aphis 
which causes such terrible destruction to the vines 
of Southern Europe and those of North America. 
Phylloxera vitis has two entirely different habits of 
life and form. In one condition it is active and winged, 
feeding upon the green leaves and shoots of the 
grape vine, where eventually it oviposits ; in the other 
condition the larva is sluggish, apterous, and lives 
^ The dimorphism of this insect will be fully described when we 
consider the genus Ohaitophorus in YoL II of this Monograph. 
