26 TEXT-BOOK OF ENTOMOLOGY 



INSECTA (HEXAPODA) 



We are now prepared to discuss the fundamental or essential 

 characters of the insects, including the wingless subclass (Synap- 

 tera), and the winged (Pterygota). 



Diagnostic characters of insects. Body consisting of not more th/i/i 

 twenty-one segments, ivhich are usually heteronomous or of unequal size 

 <ii/il shape, arranged in three usually well-defined regions; i.e. a head, 

 thorax, and hind-body or abdomen. Head small and fattened or 

 rounded, composed of not less than, six segments, and bearing, besides 

 the eyes, at least four pairs of jointed appendages; i.e. one pair of 

 antennae, and three pairs of masticatory appendages, the distal or molar 

 portion of -which is primarily divided into three divisions, supported on 

 a stipes and cardo, and in certain orders modified into piercing or suck- 

 ing structures. The head is composed of an epicraninm, bearing a dis- 

 tinct clypeus and labrum, with the epipharynx. Mandibles 1-joiuted, 

 tv it ho tit a palpus and very generally with no, or uncertain, traces of a 

 lacinia and a stipes. Two pairs of maxillce; the first pair separate, 

 usually 3-lobed, comprising a lacinia, galea,, and palpifer, with apafyws 

 ivhich is never more than 6-jointed. T7ie second pair united to form 

 the labium or under Up, composed of two lacinice fused together; in the 

 generalized forms with a rudimentary galea; bearing a pair of palpi, 

 never more than 4-jointed; with paraglossce sometimes present. 



(A thin! pair of mouth-appendages situated between the antennae and 

 mandibles in the embryo of Anurida, and A2)is, and adult Campodea.} 



The epipharynx forming the roof of the mouth, and bear ing gustatory 

 organs. Hypopharynx usually well developed, lying on the under side of 

 the mouth, just above the labium, and receiving the end of the salivary 

 duct. 



Eyes of two kinds : a pair of compound, and from two to three simple 

 eyes (ocelli'). 



The thorax consisting of three segments, the two latter segments in the 

 winged orders highly differentiated, into numerous tergal and lateral 

 pieces and a single stern mu ; in tie Symi/ttera the segment* are undi- 

 vided. (In the higher Hymenoptera the basal abdominol segment coa- 

 lesced ivith the thorax.) Three pairs of legs, each foot ending in a pair 

 of claws. Two pairs of wings (except in the Syu<ipfcra), a pair to each 

 of the two hinder thoracic segments; the wings occasionally reduced 

 or wanting in certain adaptive forms, ivhich, however, had ivinged 

 ancestors. 



Abdomen consisting at the most of from ten to twelve segments. No 



