COLORATION IN POUSTES. 31 



than that of the female. This expresses itself both in the width of the 

 median yellow stripes and the condition of the lateral yellow stripes. 

 As might be expected, there is close correlation between these two 

 markings of the metathorax. 



The metathorax is the only part of the thorax which varies con- 

 spicuously in P. variatus or in its two allies, P. auri/er and P. pallipes. 

 There is an irregular spot on the mesopleura which varies slightly in 

 size, shape, and position, its most usual form being a triangle elon- 

 gated in an antero-dorsal and postero-ventral direction. There is also 

 slight variation in the width of the borders of mesothorax, scutellum, 

 and post-scutellum. In general the yellow zone of the last is about 

 three times as broad as that of the scutellum, and, further, the yellow is 

 slightly more conspicuous in the light-colored than in the dark-colored 

 lots; but the differences are not important in specific relations, so they 

 may, for the purposes of this research, be disregarded. 



CORRELATION BETWEEN MARKINGS OF APPENDAGES AND MARKINGS OF 



ABDOMEN. 



There is conspicuous sexual dimorphism exhibited in the ventral sur- 

 face of the thorax and the coxae of the appendages. In the males these 

 surfaces are predominantly yellow ; the coxae have dark borders, and 

 occasionally the most posterior pair are black or bear traces of black. 

 In the females the corresponding surfaces are black, the coxae bor- 

 dered with yellow, and occasionally the ventral surfaces variegated 

 with yellow. For the dorsal surface of the coxae the conditions are 

 reversed. In each there is an external yellow border and a yellow 

 spot near the articulation with the trochanter. In the males the 

 former is usually narrow, leaving the greater part of the area black. 

 In the females it is broad, almost covering the dorsal surface. 



In both sexes the dark pigment occurs in the proximal end of the 

 femur, the distal end of the tibia, and the terminal tarsal joints. The 

 rest of the appendage is a dull, brownish straw-color. From these 

 points the pigment spreads, so to speak, in a varying degree in the 

 femur distally and in the tibia proximally, but in all cases the joint 

 between the two, the knee, remains light colored. In the males, 

 however, the color is confined to the outer (postero-dorsal) surface of 

 the appendage. In the females, it is most extended on the inner 

 (antero-ventral) surface of the femur, but occurs also on the postero- 

 dorsal surface. In the tibia the males agree with the females in hav- 

 ing the pigmental area on the outer surface. In the determination of 

 the correlation between the light and dark character of the body and 

 that of the appendages, the males and females are considered separately. 



