THE CHARACTERISTICS OF INSECTS. 



227 



12 3 4 



Fig. 5. 1. Nympha of Cockchafer, seen from above. 2. 

 Nympha seen from below. 3. Nympha of Oerambyx. 

 4. Chrysalis of Bombyx. 



same way. Insects of complete metamorphosis act very differ- 

 ently : the larva becomes stationary and ceases to take food ; the 

 skin becomes like parchment, and slight movements of the ab- 

 dominal rings, Avhen they are touched, are the only signs of life. 

 Yet, from the beginning of the transformation, on the seemingly 

 half-dead being, appear distinctly, although masked by a thick 

 veil, the antenna, wings, and legs. These organs are symmetri- 

 cally folded along the 

 body, and the motion- 

 less nympha under the 

 veil presents the forms 

 of the perfect insect. It 

 remains sometimes fast- 

 ened to a wall or hang- 

 ing from a branch by 

 one of the silky threads 

 which the larva has 

 woven ; in other cases 

 it is enveloped in a firm 

 shell or surrounded by 

 a silken cocoon. Nym- 

 phae thus protected remain in the open air, while others, less well 

 guarded, find shelter from bad weather and the direct force of the 

 sun often by being buried deep in the ground. 



The insect secures its release from its nymphal envelope at 

 the expense of violent muscular efforts. Sometimes the envelope 

 splits in the back and gives passage in succession to the thorax, 

 the head, the legs, and the wings ; sometimes the hinged lid or 

 operculum which closes the shell gives way under the pushing of 

 the prisoner. At the moment of emerging, the young animal is 

 not able to fly ; its wings are crumpled and soft, but the circulation 

 soon becomes more active, the wrinkles vanish, and the wings ac- 

 quire sufficient consistency to permit the new being to take flight. 



As we have already seen, the body of the adult insect may be 

 divided into three principal and distinct parts the head, the 

 thorax, and the abdomen. The head (Fig. 6) bears the mouth, 

 antennse, and eyes ; the three pieces that follow are. the three 

 united rings that constitute the thorax. After the thorax comes 

 the abdomen, the rings of which are movable and capable of 

 gliding upon one another. 



The head may be divided into several regions, which it is im- 

 portant to define well. They are, in fact, of great assistance in 

 the description and determination of species. They are four in 

 number : the front, including the space between the eyes ; the 

 vertex, or upper part of the head, behind the eyes ; the cheeks, 

 below and in front of the eyes ; and the epistoma, sometimes called 



