240 BULLETIN^ 15 7, U. S. NATIONAL MUSEUM 



If we disregard the usually strong effect of the thick costal vein 

 as being possibly due to pressure against the plate, the strongest 

 effect is produced in practically all cases by the apical portions of 

 the fore wings and more or less of their outer border (pi. 64, fig. 1), 

 while the inner (lower) margin of the fore wings gives the least 

 effect. In some cases the wings are brightly outlined when there 

 seems to be no reason for this in the color pattern (pi. 63, fig. 4; pi. 

 64, fig. 4). 



Nearly all the species tried gave equally good and strictly com- 

 parable results, but some interesting discrepancies were noted. 



In the males of the skippers of the subfamily Hesperiinae the 

 patches of androconia come out with great brilliance (pi. 63, fig. 8), 

 probably on account of the greater thickness of the wing here and 

 the resultant pressure. 



The upper surface of Pieris rapae (pi. 59, fig. 9) affects the plate 

 as if it were a very dark instead of a white insect, the image being 

 much brighter than that of the dingy underside (pi. 59, fig. 10). 



The upper surface of the males of both of the common blues {Lycae- 

 nopsis argiolus pseudargiolus and Everes comyntas^ pi. 62, fig. 9) 

 gave surprisingly bright and distinct images. 



In fresh examples of Papilio phUenor the whitish spots on both 

 surfaces acted as if they were black (pi. 62, fig. 6), but in old and 

 worn examples the whitish spots acted normally. In Papilio parts 

 and in P. polyctor (pi. 64, fig. 4) the iridescent green areas affected 

 the plates much more intensely than the dark-brown ground color of 

 the wings. Reversal of color values in swallowtails, and also in the 

 closely related parnassians {Parnassius) , has previously been noted. 



In order to ascertain the nature of the emanations affecting the 

 photographic plates, (1) exposures were made with the glass side 

 of the plate in contact with the wings ; (2) portions of the wings were 

 covered with exceedingly thin cover glasses ; (3) portions of the wings 

 were covered with strips of cellophane, which has the property of 

 being far more transparent to light of very short wave lengths than 

 glass; and (4) portions of the wings were covered with bits of quartz 

 ground down to a thickness of 0.2 mm., which were very kindly loaned 

 by Dr. W. W. Coblentz, of the Bureau of Standards. 



The exposures made with the glass side of the plates in contact 

 with the wings were uniformly negative. 



The cover glasses completely obliterated the portions of the wings 

 covered by them. 



The strips of cellophane had a surprisingly slight effect upon the 

 image made by the portions of the wings covered by them. Their 

 position was indicated simply by a slightly lighter band across the 

 wing. 



