HEMIPTERA 691 



monstrously swollen. Ocelli are often present. The antennae 

 are small with 3-25 segments. The prothorax is large, in some 

 cases monstrous, and free. The meta- and meso-thorax are 

 well developed. The tarsi usually have three segments. The 

 abdomen usually consists of 9, 10, or 11 segments. Its margins 

 are often produced into a kind of shelf which enhances the flat 

 appearance of many bugs. In Coccidae the number of segments 

 is reduced. There are 3 thoracic and 7 abdominal stigmata in 

 the Heteroptera. In many cases the female is provided with an 

 ovipositor consisting of processes from the 8th and 9th segments. 



Salivary glands are present, and also, in some cases at least, 

 a special organ or syringe for forcing out the secretion 

 which almost certainly sets up the irritation which ensues on a 

 bite. There is a fine oesophagus and a crop but no gizzard. The 

 number of malpighian tubules is small, usually four ; but the 

 Coccidae have only one pair and the Aphidae none at all. The 

 nerve ganglia are few, the infra-oesophageal may be widely 

 separated from the supra-oesophageal ganglion and may even 

 fuse with the thoracic nerve mass. 



The characteristic odour of bugs is due to the secretions of 

 certain stink-glands which in the young open on to the upper 

 surface of the abdomen and in the adults open on each side of 

 the meta-sternum. 



In many of the larger forms of Hemiptera the young hatch 

 out very like their parents, but minus the wings. In the 

 Homoptera however there is a more or less marked meta- 

 morphosis which reaches its fullest development in the Coccidae. 

 Even in the Heteroptera there is usually a considerable change 

 of colour and often of form between the young and old, and the 

 change between the final or adult form and the preceding instar 

 is often abrupt. 



The order as a whole is injurious to human activity. A few 

 destroy other harmful insects, but in the opinion of a well known 

 authority " if anything were to exterminate the enemies of 

 Hemiptera, we ourselves should probably be starved in the 

 course of a few months." 



Sub-order 1. HETEROPTERA. 



Wings partly horny, partly membranous ; anterior part of head not touch- 

 ing the coxae ; the scutellum of the mesonotum is large. 

 There are about 430 British species of this sub-order. 



