OUTLINES OF ENTOMOLOGY. 99 



The insects of this Order display great differences of form and 

 habit, but as all subsist solely on liquid nourishment, extracted from 

 living plants or animals, all the principal representatives agree per- 

 fectly in the structure of the mouth. This consists of a strong, three 

 or four-jointed beak, which is a modification of the under lip into a 

 channeled brace in which rest two pairs of very fine bristles, corres- 

 ponding to the two pairs of jaws, the combination being an admirable 

 arrangement for piercing and sucking. (In some of the more lowly 

 organized members of this Order, there is no horny -jointed beak, but 

 the front of the head is merely elongated, forming a sucker-like cup 

 provided with minute biting organs.) The upper lip (labruin) is con- 

 solidated with the lower part of the face to form a strong support to 

 the developed mouth parts. The eyes are large and round, in some 

 cases brightly colored, and two ocelli may be distinguished in many 

 species. The antennae are usually thread-like or bristle-like, in some 

 cases quite long, with the terminal joints slightly enlarged. 



In their general form the Hemiptera are among the most variable 

 of insects. Some have the body almost hemispherical, others are thick 

 and square or oblong, while others still are ^ery long and slender. 

 There is no general plan on which the joints of the thorax are devel- 

 oped, some having the pro-thorax crowded down out of sight from the 

 upper side, while in others it is very large and conspicuous. The meso- 

 thorax is usually the least variable division, except as to the scutellum, 

 which is sometimes so large as to extend backward almost to the tip 

 of the abdomen. The six legs are always present and the feet are three- 

 jointed; some terminate in a very distinct claw or pair of claws with 

 cushions (pulvilli] between them, while in others these appendages can- 

 not be distinguished. The upper wings, sometimes termed hemelytra, 

 in the typical bugs lie flat upon the back, the transparent or trans- 

 lucent tips overlapping, appearing as though crossed in the middle. 

 In other forms they are altogether membranous or coriaceous, and fold 

 roof like over the body. 



In this and the remaining Orders the transformations are usually 

 incomplete, the pupa being as active and as voracious as the larva or 

 the perfect insect. These Orders are termed inferior, not only on 

 account of the less distinct metamorphosis, but also because of the 

 many lowly organized forms which they include. 



Hernipterists are not agreed as to the primary subdivisions of the 

 Order, some finding it more convenient to consider the various forms 

 under three Sub-Orders, while others find it necessary to define five. 



