THE YOUNG NATURALIST. 89 



If a wing be cut across during the life of the insect, the nervures do 

 not bleed : but apply considerable pressure between two plates of 

 glass, and a viscid, homogeneous mass exudes. 



The expansion of the wings is materially assisted by the insect 

 resting in a perpendicular position, usually on a wall, fence, or tree 

 trunk, the head being uppermost, and the weight of the wings acting 

 downwards. 



The development generally takes place at night or early morning, 

 though much depends upon the hour of the day devoted by the insect 

 to the use of its wings. Some spot sheltered from the direct rays of the 

 sun is usually selected, to avoid any risk of the membranes becoming 

 dry and hard before being completely expanded, and so crippling 

 the creature for life. Even under the most favourable auspices, there 

 may be failure in development arising from weakness, and consequent 

 inability to force the vivifying fluid through the hollow nervures. 

 Sometimes a wing is absent, nor can the slightest trace of it be dis- 

 covered : this is a true monstrosity, and should be preserved as such. 

 Or, again, one or more wings, having received some injury, possibly 

 owing to the nervures being choked, or a crease or fold beyond the 

 power of the insect to straighten, occurring at the roots, the result is 

 known as a cripple. 



We may now consider the positions and number of the wings, 

 adding a few remarks upon the terms used in distinguishing one part 

 of the wing from another. Those members, whether two or four in 

 number, are attached to the thorax, or second great division of an 

 insect's body. The thorax is again divided into three chief parts: 

 the pro-thorax, meso-thorax, and meta-thorax. 



The pro-thorax is never provided with wings, and is usually small, 

 being cramped and contracted to make room for the powerful motive 

 muscles contained in the two other segments ; and in all insects hav- 

 ing four organs of flight, the anterior pair are affixed to the meso- 

 thorax, and the posterior couple to the meta-thorax — in both cases, 

 one on each side. In some orders, such as the lepidoptera and 

 hymenoptera, the roots of the anterior wings are protected by a pair 

 of scales termed tegulcz, but I will merely mention them, as they are 

 not attachments to the wings, and consequently need no further 

 reference. 



In the typical wing, the root or place of attachment to the thorax 

 is termed the base ; the upper or outside edge, the costal or anterior 

 margin ; that portion nearest to the abdomen when the wings are laid 

 at rest, is called the interior or inner margin ; and that part of the wing 



