362 ZOOLOGY 



This order comprises numerous insects familiarly known 

 as bugs or lice. They present very great variety of form, 

 some of them having short soft bodies with almost every trace 

 of segmentation lost, whilst others are large and hard. 



The mouth parts are adapted for taking up fluid. The 

 labium is modified into a jointed sheath which guards the 

 other appendages ; at its upper end the hollow structure is 

 closed by the labrum. Within the tube thus formed lie four 

 rigid stylets, which represent the two mandibles with sharp- 

 ened tips, and the two anterior maxillae of unequal length 

 with serrated edges. The maxUlary palps are absent and the 

 labial palps are very small. 



The antennae are short and three-jointed, or long and 

 multiarticulate. The eyes are usually small ; sometimes two 

 otelli are present. In the larger species the body is very 

 often flat and angular in outline. There are usually four 

 wings, rarely only two, and sometimes they are entirely want- 

 ing. In the former case the anterior wings have their basal 

 half horny and their distal half membranous, whilst the pos- 

 terior wings are membranous (Heteroptera), or both pairs are 

 membranous (Homoptera). 



The legs are usually of the walking type, the tarsus is 

 two- or three-jointed. The lateral margin of the abdomen is 

 greatly developed in some species. The stigmata are usually 

 conspicuous ; in the aquatic species there are a pair at the end 

 of the abdomen, often borne at the tip of long processes. 



The Hemiptera in most cases emit a fluid with a very dis- 

 agreeable smell. This is secreted from a pair of pores on the 

 under surface of the thorax, near the coxae of the middle pair 

 of legs. This objectionable fluid is defensive in function. 

 Other members of the group produce considerable quantities 

 of wax, which is secreted by unicellular cutaneous glands. 



The young resemble the adults, but are without wings. 

 The males of the Coccidae alone form pupae within a cocoon, 

 and thus undergo a complete metamorphosis. 



The Hemiptera are divided into three sub-orders : 



1. Heteroptera. 



2. Homoptera. 



3. Parasitica. 



