70 Psyche [April 



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 exuvise, 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 exuvise. 



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 fhght 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 



