68 
Psyche 
[April 
rupture to the final escape of the insect, lasts from about twenty 
to about thirty minutes. 2 The freshly molted aphid is at 
once able to walk, but is incapable of resuming feeding until 
about one-half hour, or more, later. 
One other point may be noted here in connection with ecdysis 
The layers of the black pigment which in this species give the 
antennae, haustellum, wing-pads, legs, cornicles, and abdominal 
cauda their characteristic piceous color are intimately associated 
with the chitinous exoskeleton, and are cast off with the exuviae 
at each molt. They are then formed anew in the succeeding 
instar. The freshly molted Macrosiphum tanaceti is uniformly 
light green, except the eyes, which are reddish vermillion. The 
light green color is due to the presence of characteristic green 
substance in the fat cells and other body tissues, which shows 
through the semitransparent cuticle. This coloring matter has 
been the subject of investigation years ago by various workers, 
notably by Macchiati (1883), who claims to have found chloro- 
phylloicl substances in Siphonophora malvce and in S. rosce, and by 
Przibram (1906, 1909), who has observed that aphids fed on 
etiolated leaves of onion plants that have been kept in the dark 
assume the pale yellow color of the latter, suggesting thereby 
that the green chlorophyll of the plant probably has some relation 
to the green substance in the aphid tissue. More recently, 
Glaser (1917) has reported that by chemical tests he has been 
able to detect the presence of red pigments in Pterocomma 
smithies Monell which seem to be localized in the cytoplasm of 
the fat cells, and which give color reactions suggestive of an- 
thocyanin found in plants. 
The characteristic piceous color of the exoskeleton in the 
regions enumerated above is restored in less than an hour after 
molting. How this relatively rapid change in color is brought 
about is difficult to explain. Two possible conditions suggest 
themselves: (1) After molting, these pigments, with their de- 
finitive dark color, are segregated as such by some very active 
plyysiological process; or (2) prior to, or during, molting the 
„ 7 2 About the same length of time has been observed in Toxoplera graminum Rondani by 
Webster and Phillips (1912). 
