150 PROTECTION AGAINST INSECTS. 



and four pairs of legs; abdomen destitute of limbs; no 

 antennae. Scorpions, spiders, and mites. 



3. Myriapoda : respiring by tracheae, or involutions of the 

 integument ; head distinct, remainder of the body formed of 

 nearly similar segments ; one pair of antennae ; three pairs of 

 jaws and numerous legs. Centipedes, millepedes. 



4. Insecta : respiring by tracheae ; head, thorax, and 

 abdomen .distinct, one pair of antennae ; three pairs of legs 

 on the thorax ; abdomen without well-developed limbs ; 

 generally with two pairs of wings on the thorax. Insects. 



A knowledge of the general anatomy of insects, and of the 

 terms used in the present book in describing the different 

 species, is presupposed. 



Insects as a general rule before attaining maturity pass 

 through a series of changes termed metamorphoses. 



The different stages of their life consist of the egg, larva, 

 pupa, and imago or perfect insect. Some insects, such as 

 parasitic lice, do not appear to undergo any metamorphosis, 

 the young on hatching-out resembling their parents in all 

 respects except in size, although they may moult, or shed their 

 skins frequently ; they are known as ametabolic insects. 



The larval stage is essentially the stage of growth and of 

 active feeding. The larva undergoes several moults or ccdyscs, 

 never possesses wings and is incapable of reproduction. 



The larvae of insects may be destitute of legs, as in the case 

 of fly maggots, or they may have three pairs of true legs, on 

 the first three segments after the head, as in the cockchafer 

 grub, or in addition to these, two, five, six, or seven pairs of 

 clasping feet, or prolegs attached to the abdominal segments, 

 of which the pair on the last segment are known as the anal 

 prolegs or claspers. The larvae of 'Lepidoptera are termed 

 caterpillars. 



The pupa of insects is usually inactive, and is protected by 

 its dried and hardened skin ; frequently, as in spinning 

 Lepidoptera, it is surrounded by a protective case termed a 

 cocoon, and constructed by the larva. 



In the case of certain insects, as grasshoppers, the pupa 

 differs from the larva only in having rudiments of wings ; it 

 is still active and feeds, and is termed a nymph. Such a pupa 



