METAZOA INSECTA. 473 



head; there are no ocelli, though each compound eye is 

 made up of an immense number of single eyes. 



The antennae (No. 1207 ; PI. 1206, fig. 7) are knobbed, 

 the typical character of butterflies, as already stated. 



Remarkable modifications in structure have taken place 

 in the mouth parts, suggestive of equally great changes 

 in the habits of these insects in some remote past. 



The mandibles described in the young butterfly have 

 become obsolete, consisting only of tiny plates (PL 1206, 

 fig. 6, md) immovably fastened to the head. The first 

 pair of maxillae has taken upon itself the function of 

 sucking nectar from the corollas of flowers, and has 

 become a long spiral organ (fig. 7, mx'}. The palpi (fig. 

 7 1/") f the second pair of maxillae have become brushes 

 for aiding the insect in obtaining nectar. 



The reduction of the prothorax indicates that the first 

 pair of legs are of little or no use, and this is the case, 

 since they do not even support the insect when it alights 

 but are folded across the breast. The first section is 

 supplied thickly with hairs, hence the name of Nympha- 

 lidae or brush-footed butterflies. The remaining legs are 

 weak and are of no service in locomotion but simply in 

 supporting the insect. 



The chief character of the wings is the coating of scales 

 which are modified hairs. This peculiarity has given the 

 order the name of Lepidoptera, meaning scale and wing. 

 These scales are striated and of different colors ; each is 

 attached by a stem or pedicel and their arrangement on 

 the wing is like that of shingles on a house. 



According to Mayer 1 the wings of Danais plexippus 

 Linn., during early pupal life, are transparent as glass, 

 and this condition corresponds to the period before the 

 scales are formed. From five to ten days before emer- 

 gence the wings become opaque and white. This condi- 

 tion is caused by the withdrawal of the protoplasm from 



1 Bull. Mus. Comp. Zool., XXIX, no. 5, 1896, p. 209. 



