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 than 

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

 and shape, arranged in three usually well-defined regions; i.e. a head, 

 thorax, and hind-body or abdomen. Head small and flattened 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 <>j 

 antenna,, 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 />i< r<-ing or suck- 

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

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

 without 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, andpalpifer, ivith a pal pus 

 which is never more than 6-jointed. TJie second pair united to form 

 the labium or under Up, composed of two lacinia} 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 third pair of mouth-appendages situated between the antenna* and 

 mandibles in the embryo of Anurida, and Apis, and adult Campodea.) 



The epipharynx forming the roof of the mouth, and bearing gustatory 

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

 the mouth, just above the labium, and receiving the end of the salt ran/ 

 duct. 



Eyes of two kinds : a pair of compound, and from two to three sin<j>l<> 

 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 sternum ; in the Synaptera the segment* arc undi- 

 vided. (In the high IT Hymenoptera the basal abdominal .^t/ni^nt <-oa,- 

 lesced with the thorax.} Three pair* of l^gs. <-a<-h foot ending in a {>air 

 of claws. Two jmirs of wings (except in the Synaptera), a pair 

 of the two hinder thoracic segments; t/' wings ocr<i*fnnally 

 or wanting in certain ada^tirc forms, which, however, had 

 ancestors. 



Abdomen consisting at the most of from ten to twelve segment*. 



