4 Transactions of the 



surface is also hackled, somewhat like that of the spider-scale I 

 have alluded to, but to a much greater extent. Perhaps some will 

 regard it as plumose. It also presents the phenomenon so common 

 to many insect scales, of decomposing the Hght which passes through 

 it, so that some portions of its fringes display gorgeous colours by 

 transmitted light, — colours more or less complementary to those 

 seen in the same scale by reflected light. 



In the scales of Polyxenus lagurus I have found what is very 

 uncommon (so far as my examinations, which have been very care- 

 fully made, are reliable), a deposit between the membranes. The scale 

 is a sohd structure, not, as in the generality of cases, merely an upper 

 and lower membrane without any intermediate deposit. The sur- 

 face-contour is uneven, swelled into elevations at regular points. 



The presence or absence of a beaded deposit between and dis- 

 tinct from the membranes of scales has formed a branch of my 

 inquiry, and I endeavoured to satisfy myself upon the point by 

 tearing open or crushing between glasses such specimens as showed 

 the phenomenon of beads in a marked manner by ordinary illumi- 

 nation. The only results I obtained on these occasions were nega- 

 tive. One of the most marked examples I have endeavoured to 

 represent. It is from one of the exotic Argynnidae, but I am 

 unable to name the butterfly whence I got it. The scale was torn 

 in such a manner as to display the interior of the upper and lower 

 membranes. There was no debris in its neighbourhood resulting 

 from the escape of any fluid matter or beads, and the damaged 

 membrane only gave evidence that its folds or corrugations were 

 destroyed. The colour of the scale was deep yellow. In all other 

 similar experiments, except where I had actually pulverized the 

 scales in my efibrts, similar negative appearances were presented. 



Thus, the investigation led me to the conclusion that whatever 

 beads (with exceptions to be noticed presently) I saw in the scale, 

 before submitting it to injury, had no real existence as heads, but 

 were due to the interference of the rays of hght by corrugated 

 membranes ; they were ghost-beads, in fact. 



A still more striking example of these ghost-beads or illusive 

 appearances is given in the iridescent scales of the beautiful West 

 Indian moth, Urania Leilus, which, like those of the Diamond 

 beetles, display chromatic effects by transmitted as weU as by re- 

 flected hght. When one of the semi-transparent scales is taken 

 (say one of those orange-red by transmitted, and metalhc-green by 

 reflected hght), and the surface next the object-glass accurately 

 focussed, an appearance like A in the illustration is seen ; but if 

 the focus be altered so as to penetrate into the scale, views resem- 

 bhng B, C, and D are given (Plate LXX.), according to the depth 

 to which we try to penetrate our glance into the interior of the 

 scale and the quality of the illumination we use. 



