5 THE BUTTERFLIES OF THE BRITISH ISLES. 



whilst a very important function takes place. This is the 

 distention and drying of the wings, which at first are very weak 

 and somewhat baggy affairs, although the colour and markings 

 appear upon them in miniature. All other parts of the butterfly 

 seem fully formed, but the helpless condition of the wings alone 

 prevent it as yet from floating off into the air. In a remarkably 

 short time, after the insect has settled to the business, the fluids 

 from the body commence to flow and circulate through the 

 wings, and these are seen gradually expanding and filling out 

 until they attain their proper size. Occasionally there is some 

 obstruction to the equal distribution of the fluids, and when this 

 occurs a greater or lesser amount of distortion, or cockle, in 

 the wing affected is the result. When the inflation is com- 

 pleted the wings are kept straight out for a time ; they are then 

 motionless, but all their surfaces are well apart. The wings 

 being now fully developed, the further flow of fluid appears to 

 be arrested. It has been stated by some authorities that this 

 fluid is fibrin held in solution, and that when the work of ex- 

 pansion has been accomplished, the watery medium evaporates, 

 leaving the fibrin to harden, and so fasten together the upper 

 and lower membranes of the wing and to fix the veins, or 

 nerves, in their proper position. Mayer, a specialist on these 

 matters, referring to the expansion of the wings, remarks that 

 the blood [the fluid previously mentioned] forced into the freshly 

 emerged wing would cause it to become a balloon-shaped bag 

 if it were not for fibres that hold the upper and lower walls 

 closely together. The fibres referred to, he states, are derived 

 from those hypodermic cells which do not contribute to the 

 formation of scales, but are stretched out from one wall of the 

 wing to the other. 



It may be well now to briefly consider some of the structural 

 details of the perfect butterfly, so a beginning will be made with 

 the head (Fig. 6). When looking at the head of a butterfly, 

 the first thing to attract the attention is the very large size 



