70 
Psyche 
[ApYil 
during the process. The rupture of the chitinous exoskeleton 
appears first near the base of the clypeus and extends dorsome- 
dially to the posterior margin of the metanotum. The entire 
molting process, from the formation of the initial rupture until 
the aphid extricates itself, lasts about thirty minutes. It is able 
to walk soon after escaping from the exuviae, but is incapable of 
resuming feeding until about one-half hour, or more, later. 
The characteristic piceous color in certain parts of the body 
is either located in, or intimately associated with, the chitinous 
exoskeleton, and is cast off at each ecdysis, reappearing, however, 
in the newly formed integument in less than an hour after molting. 
The light green color which characterizes the larger portion of 
the body is due to certain substances in the fat cells showing 
through the semitransparent cuticle. 
The new chitinous layer is deposited sometime before the 
molt. It has a chance to harden during the lengthy process of 
casting off the old exuviae. 
II. Locomotion. The principal and usual method of loco- 
motion, even in alate individuals, is by walking. The wings are 
used very rarely, and perhaps in connection only with migration 
from one plant to another when the aphids on a particular host 
begin to become overcrowded or when the supply of plant sap 
becomes inadequate. The flight is very feeble, and it is doubtful 
if the insect can traverse any considerable distance by this means 
alone. 
In walking, the antennae are directed anteriorly, describing 
in that position an angle of about forty-five degrees. They con- 
tinually sway obliquely in alternate turns in an entodorsal and 
ectoventral direction. The rate of this movement is apparently 
correlated proportionately with that of the legs; and under 
ordinary conditions, when the insect is not disturbed, or other- 
wise excited, the antennae sway one hundred and twenty times in 
one minute. This figure has been found to be approximately 
correct for all instars. 
After numerous attempts at following the movements of 
the legs while the aphid is walking, I have come to the conclusion 
