68 Psyche ■ [April 



rupture to the final escape of the insect, lasts from about twenty 

 to about thirty minutes.^ 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- 

 phjdloid 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 

 smithim Monell which seem to be locahzed in the cytoplasm of 

 the fat cells, and which give color reactions suggestive of an- 

 thoc3^anin 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 

 physiological process; or (2) prior to, or during, molting the 



2About the same length of time has been observed in Toxoptera graminum Rondani by 

 Webster and Phillips (1912). 



