LoS) 
ON 
to 
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 joimted 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 maxillary 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 
ocelli 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. 
