xlii .LLOYD'S NATURAL HISTORY. 



saic pattern may contain 870 tesserulae, in separate pieces, in 

 one square inch of surface; but the same extent of a Butterfly's 

 wing sometimes consists of no fewer than 100,736 !" (Duncan.) 



In addition to the ordinary scales, the males of many Butter- 

 flies possess special additional scales, smaller than the others, 

 which have been called plumules, battledore-scales, or andro- 

 conia. Sometimes they are scattered among, and hidden 

 under, the ordinary scales, but they are frequently placed in 

 masses on a particular part of the wing, and covered by large 

 overlapping scales. They are generally colourless, but some- 

 times black or brown. Not unfrequently they are concealed 

 in a pocket or fold of the wing. They are generally longer 

 and softer than the ordinary scales, and evidently serve as out- 

 lets for scent-glands in the tissue of the wing.* 



The scales are considered to be modified hairs, and consist 

 of double-walled closed sacs, which afterwards flatten out, and 

 are striated. The colour of the wings of the insect is partly 

 due to pigment contained in these sacs, and partly, especially 

 in the case of shot or iridescent tints, to the refraction of 

 light from the striated scales of the wing. 



In many Butterflies and Moths, more or less of the wing, 

 from a few small spots, to the whole surface except the borders, 

 is colourless. This is the case in our Bee Hawk-Moths, and 

 Clear-wing Moths ; but though only one genus of European 

 Butterflies (Carcharodus) exhibits even as much as a few trans- 

 parent spots on the wings, many South American genera of 

 different groups (Ithomia, Hetara, Zeonia, &c.) have the wings 

 as colourless as in our Clear-wing Moths. But in the case of 

 the Bee Hawk-Moths, and probably of many other transparent- 

 winged Lepidoptera, the insect, on emerging from the pupa, is 

 slightly clothed with loose scales over the transparent part of the 

 wings, which soon rub off. 



* See Thomas, "American Naturalist," vol. 27, p. 1018 (Novem- 

 ber, 1893). 



