PLANT LICE. 145 
“In addition to honey-dew, many Aphids excrete a white 
substance. ‘This may be in the form of a powder, scattered over 
the surface of the body, or it may be in large flocculent or downy 
masses; every gradation between these forms exists. 
“The plant-lice are remarkable for their peculiar mode of 
development. The various species differ greatly in the details 
of their transformations; but the following generalizations can be 
made: 
“At some. period eggs are produced by impregnated females. 
This ordinarily occurs in the autumn; in which case the eggs 
do not hatch till the following spring. From the fact that these 
eggs are fertilized, they are frequently referred to as true eggs, 
in contradistinction to pseudova, described later. These true eggs 
are also known as winter eggs. 
“From the winter eggs there hatch in the spring a genera- 
tion of Aphids in which there is no distinction of sex. All are 
females; and each has the power of reproducing without the in- 
tervention of a male. Such reproduction is termed agamic re- 
production, or reproduction by budding. And this term is also 
applied to the individuals that reproduce in this way. Usually, 
the agamic generation produced by the winter eggs is wingless. 
The agamic female which hatches from a winter egg, being the 
starting point from which arise the generations that intervene 
between this egg and the production of other true eggs, is termed 
the stem-mother. 
“The offspring of the stem-mothers are wingless, or winged, 
or both, and are agamic. In many cases they are born alive. 
This can be seen by examining almost any colony of plant-lice 
during the summer time. While an agamic mother is uncon- 
cernedly feeding or walking about, it may be giving birth to a 
young louse; the latter can be seen with the unaided eye, but 
better with a lens, emerging from the caudal end of its mother, 
tail first, and kicking vigorously, even before its head has been 
delivered. In other cases, the agamic form produces egg-like 
bodies, which are termed pseudova, to distinguish them from the 
fertilized or true eggs. And, in still other cases, they produce 
living young, which are enveloped in a pellicle, from which they 
emerge in the course of a few minutes; such an enveloping pellicle 
with its enclosed young is also termed a pseudovum. 
