LEPIDOPTERA : STRUCTURE. 393 



but a few of them ; and in others, certain portions of the 

 wing exhibit small transparent patches similarly denuded, as 

 in the great atlas moth. In many species, scales exhibit me- 

 tallic tints, which, indeed, in some exotic butterflies, are so 

 exceedingly resplendent, that in the bright light of the sun 

 it is almost impossible to look upon them. In like manner, 

 several of our fritillary butterflies, and especially Lathonia, or 

 the queen of Spain, has the under surface of the lower wings 

 adorned with beautiful silvery spots. " How this remarkable 

 efi^ect of metallic lustre is produced, seems not to have en- 

 gaged the attention of entomologists. M. Audebert is of 

 opinion that the similar lustre of the plumes of the hum- 

 ming birds {Trochilus) is owing to their density, to the pohsh 

 of their surface, and to the great number of little minute 

 concave mirrors which are observable on their little beards. 

 {Nouv. Diet. d'Hist. Nat, viii. 257.) But these observations 

 will not apply to the scales of the wings of the butterflies, 

 which are always very thin, and very flat ; in some instances, 

 as in Morpho Menelaus, there appears more than one very 

 slight channel upon a scale, but this takes place also in others 

 that reflect no lustre. Their metallic hues must, therefore, 

 principally be occasioned by the high polish of their siu-face 

 and the richness of their tints. It is the pm-ity of the white, 

 in conjunction with their shining surface, contrasted with the 

 dull opaque colour of the under side of the secondary wings, 

 that causes the spots that decorate those of the fritillaries to 

 emulate the lustre of silver." {Introd. to Ent., vol. iii, p. 652.) 

 The curious apparatus, consisting of a loop and a strong 

 bristle, whereby the two wings on each side are retained 

 together, is found in many of these insects, and indeed is not 

 met with in any other order. The loop is formed either by 

 an elevated portion of the membrane of the strong central 

 nerve of the upper wing, or by a little tuft of raised hairs. 

 M. Poey has observed that it is simple in the males, but 



