INSECTS. 



263 



cies which have a cocoon the silken threads are softened 

 by fluids secreted by the imago, and in some there are 

 hooks at the bases of the wings which aid in tearing an 

 opening for the escape of the moth. 



When the imago first comes out it is soft and flabby, 

 and the wings are soft bags. They are rapidly distended 



FIG. 82. Army-worm moth (Leucania unipuncta). From Riley. 



by blood pumped into them, and, held expanded, are 

 rapidly dried by the air into efficient organs of flight. 

 The wings are covered with scales, and to these the color- 

 pattern is due. These scales are merely modified hairs 

 like those which cover the whole body. When removed 

 the wing is seen to have a framework of supporting nervures 

 or ' veins' which are really not veins at all. These veins 

 vary greatly in their arrangement in different moths and 

 butterflies, and are used as a basis of classification. 



While the larvae are biting insects, the adult is adapted 

 for taking liquid nourishment by means of a so-called 

 'tongue' which when not in use is coiled beneath the head 

 like a watch-spring. This tubular structure, which, in 

 function, is so like the beak of the bugs, is much different 

 in structure, as it is formed by the union of the two max- 

 illae, while the other parts labrum, mandibles, maxillary 



