INSECT VARIETY. 



91 



marg'iu is also strengthened in swift-flying insects. The un- 

 folding of the wings is accomplished by inflation of its veins, 

 virtually prolongations of the tracheae ; and their expansion is 

 performed by one set of muscles placed centrally and horizontally, 

 their elevation and dej)ression by others obliquely vertical, and 

 situated laterally in the thorax. There are also rotator muscles. 

 The wing has an intricate articulation, and when this is mem- 

 braneous it is covered or protected by a little scale ; cheek 

 ligaments are likewise present to regulate its action. The fore 

 and hind wings may be considered as representing in movement 

 the primary and secondary quill feathers of Aves. But a varia- 

 tion in outline we associate with a chanffe of character in flight. 



Fig. 1. Outline of the wing in Skimming Insects. Examples: Polyommatus, 

 Vanessidse. 



Fig. 2. Outline of the wing in Skipping Insects. Examples : Pieridae, Tortricina, 

 Hesperidse, Liparidaj, Bombycidae, Saturnidse, Ourapteryidse. 



Fig. 3. Outline of the wing in Soaring Insects. Examples : Papilio, Apatura, 

 Morpho. 



Fig. 4. Outline of the wing in Insects that Hover. Examples: Syrphidae, 

 Anthomyiidse, Bombyhus, Culex, Ceratopogon, Chii-onomus, Psychoda, Formicidae, 

 Termites, Sphingidae, Sesiidas. 



Fig. 5. Outline of the wing in Insects that Dance. Examples : Trichocera, 

 Helicouia, Hepialus, Adela, Nemophora, Ephemeridffi, Trichoptera. 



Skimming insects (Fig. 1) have broad and rounded wings, 

 with ample sustaining area. Skippers (Fig. 2) are characterised 

 by a blunt or falcate wing, and their flight may be compared to 

 that of short-winged birds, but the Soarers (Fig. 3) have wings 

 of greater breadth and are more triangular, inviting comparison 

 with acute-winged birds ; hollow lines, such as we see in the 

 Brimstone Butterfly, appear to favour concealment by allowing 

 the species to settle suddenly. 



