HOW THE WINGS ARE FOLDED 



155 



the head joint when the wings snap back upon the back. The mechanism which 

 causes this turning is, however, of a somewhat complicated nature. The most 

 instrumental part of it is the powerful elastic band (#) which is stretched over 

 from the hinder edge of the mesothorax (J? 2 ) towards that of the wings. This 

 membrane is extended by the expansion of the wings, and draws them towards 

 the body as soon as the contraction of the muscles relaxes. This closing band 

 of the wings is assisted by a leverage system consisting of three little chitinous 

 rods (c, d, e), which at its joining presses inwards on the body on one side, and 

 on the hinder edge and head-joint of the wing on the other. 



We must, however, lay great stress on a few more kinds of wing support. 



The wing-cases of beetles at their return from flight are joined together like 

 the shells of a mussel on the inside as well as to the wedge-shaped plate 

 (Fig. 170, schi) between faschi 



their bases. There is even 

 a kind of clasp at hand for 

 this purpose. The base of 

 the wing, that is, bears a 

 pair of tooth-like projections 

 (), which fit into the cor- 

 responding hollows of the 

 little plate. 



The commissure arising 

 from the joining of the inner 

 edges is characteristic. Usu- 

 ally the wings on both sides 

 interlock by means of a 

 groove, as in stag-beetles, 

 but sometimes even, as in 



,. , . , FIG. 170. Mesothoracic skeleton of a stag beetle: MM, 



(..lilamys, alter the mann r scutellum, on each side of which is the articulation of the fore 



wing ( V), consisting of two small styliform processes (>, h) of 

 the base of the wing ; an, tooth which fits into the cavity of 

 the wing-lock (gr) ; I, edge of the right wing, passing into the 

 tion Of the two most prev- corresponding groove (fa) of the left ; Di, diaphragm for the 



attachment of the tergal muscle of the metasternnm ; MI (not 



alent methods Which the explained by author); Ka, acetabulum of the coxa (Ifu); Se, 

 Cabinet-maker uses iu join- chitinous process for the attachment of the coxal muscle ; Fe, 



femur; Soft, tibia; _g 2 , sternum. After Graber. 

 ing boards together. 



The act of folding the broad hind wings among beetles is not less significant 

 than the arrangement of the fore wing. If we forcibly spread out the former in 

 a beetle which has just been killed and then leave it to its own resources again, 

 we observe the following result : According to its peculiar mode of joining, the 

 costal vein on the fore edge approaches the mid or discoidal vein of the basal 

 half as well as the distal half of the wing, whence arises a longitudinal fold 

 which curves in underneath. Then the distal half snaps under like the blade of 

 a pocket knife and lies on the plane of the costal edge of the wing, while it also 

 draws after it the neighboring wing-area. The soft hinder-edge portion turns in 

 simultaneously when this wing-area remains fixed to the body while the costal 

 portion is moving towards the middle line of the body. 



The wing-membrane of almost all insects have, moreover, the capability of 

 folding themselves somewhat, and this power of extending or contracting the 

 wing-membrane at will is of great importance in flight. 



Yes, but how is the folded wing spread out again ? The fact may be shown 

 more simply and easily than one might suppose, and may be most plainly 

 demonstrated even to a larger public by making an artificial wing exactly after 

 the pattern of the natural one, in which bits of whalebone may take the place 



of two cog-wheels, so that 

 we have here also an imita- 



