INSECTS. 137 



transparent and clear as glass. In many species (all 

 hawk-moths, many owlet moths) there is a wing-hook- 

 let, i.e. the hind wing has a spine or a thick brush 

 which grasps a band-like area of the fore wing. In this 

 way the two pairs of wings are held together. The 

 females of a few species of spinner and looper moths 

 are wingless, or only possess short flap-like wings 

 useless for flight. The metamorphosis is complete 

 (p. 89) ; the larvae are true caterpillars ; the pupse 

 are obtectate (p. 93). Many caterpillars creep into 

 the ground to become pupse, and spin no investment 

 at all (e.g. hawk-moths). Others make a cocoon, 

 which may consist of threads loosely woven together 

 or may be of firm texture (Fig. 60). The cocoon 

 consists chiefly of silk, a substance secreted in a 

 spinning gland, and exuding to the exterior on the 

 lower lip ; but minute particles of sand or earth, and 

 fragments of wood gnawed off by the caterpillar, may 

 be stuck in the cocoon. The pupse of butterflies are 

 naked, without cocoon, but are fixed by threads to 

 leaves, tree stems, walls, hedges, etc. A distinction 

 is drawn between girdled and suspended pupse ; the 

 first are fixed by a silk band, which surrounds them, 

 and the head is directed upwards, while the latter are 

 suspended by the tip of the abdomen (Fig. 94). The 

 time required for the development of the perfect 

 insect from the pupa is not always the same, depend- 

 ing not only upon the species, but also upon the time 

 of year. The summer generation of the large white 

 spends scarcely fourteen days in the pupa stage, the 

 winter generation eight months. 



Family: Diurna {Butterflies). 



Body relatively weak and thin ; wings very broad, 

 not very long relatively. No wing-hooklet (see above). 

 Wings folded together above in a state of rest, so 

 that their upper sides touch. Antennse thickened in 



