THE LEPIDOPTERA. 69 



At first sight the scales look like dust, and they come off on 

 to the finger and thumb when the wings are touched ; but under 

 the microscope they present most elegant shapes and singularly 

 elaborate details of structure. Variable according to the genera 

 and species of the Lcpidoptcra, and equally so in different parts of 

 the same wing ; the scales 'may be more or less elongated or even 

 fan-tailed in shape, and rounded at the free edge, or incised, so 

 as to resemble dentations or pointed festoons. There is a short 

 stalk at the base of each scale, which resembles a handle under 

 the magnifying power of the microscope, and it is the portion 



A PORTION OF THE WING OF Attaais pavouia major. 

 Showing tlie method of implantation of the wing scales. (Magnified.) 



which is implanted into the alar membrane. The surface of 

 the scales ordinarily presents several longitudinal keel-like promi- 

 nences, which are parallel and equidistant. Some cross markings, 

 which are very close together, form a very delicate network 

 between the keel-shaped lines, and they appear to have some- 

 thing to do with the connection between the neighbouring scales. 

 The scales are formed by two layers of excessively delicate tissue, 

 and a third layer appears to exist between these. The colours are 

 produced by extremely small dots, beads, or corrugations, which 

 act upon the rays of light, and produce the phenomena of " inter- 

 ference." There may be some special colouring matter in the 

 scales, and most of the effect is brought about by the "inter- 

 ference" and decomposition of light. Dr. Pigott and others have 

 lately shown that the so-called ribs of the scales are corrugations 

 of one or both of the layers of tissue, and that the beads— which 



