LEPIDOPTEKA. ^ 187 



pears like a part of the neck, and is free from the 

 mesothorax. The small size of this ring is one of the 

 important characters of the Lepidoptera, distinguishing 

 this order from the Thysanura, Orthoptera, Hemip- 

 tera, Coleoptera, and Neuroptera. On the upper side 

 of the prothorax are two knob-like prominences, which 

 in the living butterfly are tipped with white hairs. The 

 mesothorax (Fig. 135, /^") is large and strong. It is 

 convex above, and bears on its forward part a pair of 

 patagia or shoulder lappets {Ip), which are also pos- 

 sessed by the wasps among the Hymenoptera (see 

 p. 242). The metathorax (Fig. 135, <^"'), though 

 smaller, is nevertheless stout and chitinous. It is 

 separated from the mesothorax by a deep groove, and 

 the two rings move upon each other. In most of the 

 flying insects already observed, such as dragon-flies, 

 harvest-flies, etc., the power of flight has been cor- 

 related with a marked tendency to consolidation of 

 the thoracic region. Most butterflies offer apparently 

 an exception to this rule ; for while they are pre- 

 eminently fliers, the mesothorax and metathorax are 

 each capable of considerable freedom of motion. An 

 explanation of these facts is found in the peculiar 

 flight of this insect and the unique structure of the 

 hind-wings. The movement is slow and wave-like 

 as compared with the swift, arrow-] ike flight of the 

 dragon-fly. The long veins in the posterior part of 

 the hind-wings (see Fig. 134), not found of such 

 length in any of the insects before described, aid in 

 producing the slow, fluttering motion. If, now, we 

 could find a butterfly or moth whose flight was swift 

 and sustained, and whose hind-wings, therefore, were 



