476 THE INVERTEBRATA 



nocerata. The former are noteworthy for their numerous adaptations 

 to aquatic life. They commonly lay their eggs in the tissues of sub- 

 merged plants. Many, e.g. the water boatman, Corixa, and back- 

 swimmer, Notonecta, have powerful legs fringed with hairs which, by 

 the simultaneous movement as members of pairs, propel the animals 

 through the water as oars do a boat. They breathe air at the surface 

 film, making use either of a terminal abdominal tube (Nepa) or of 

 unwettable hairs between which air is trapped to enable the animal 

 to breathe during its periods of complete immersion (Notonecta). 



Among the Gymnocerata may be mentioned the bed bug, Cimex, 

 an ectoparasitic insect, with vestigial wings, flattened body and 

 prominent claws. It inhabits human dwellings, and its retiring habits 

 coupled with its power to fast for long periods make it a difficult 

 creature to eradicate when once it is established. The shield bugs 

 {Pentatomidae) are phytophagous. The mesothoracic tergum is greatly 

 enlarged to extend at least as far over the abdomen as the junction 

 between the horny and membranous parts of the wing when these are 

 at rest. The red bugs (Pyrrhocoridae) are also phytophagous. Certain 

 species, e.g. of Dysdercus, are known as "stainers" from their habit 

 of feeding on cotton-bolls into which they inject a micro-organism 

 responsible for the appearance of a red stain on the fibre. The 

 Capsidae are almost exclusively phytophagous, some of their members 

 being very serious pests of our English orchard trees and shrubs. 

 Plesiocoris, until recent times restricted to such trees as willow, now 

 attacks black currant bushes, apple trees, etc. An exception to this 

 phytophagous habit is found in Cyrrtohinus mundulus which sucks the 

 eggs of the sugar cane hopper, Saccharicida, so eflPectively controlling 

 this pest in Hawaii. In the family Reduviidae are many forms which 

 transmit trypanosomiasis, in the tropics, e.g. Rhodius prolixus. 



The extent to which the head flexure has brought the point of 

 emergence of the rostrum into the thoraco-sternal region forms the 

 basis for the separation of the Homoptera into two tribes. The least 

 modified from the heteropterous condition in this respect are the 

 Auchenorhyncha (Fig. 329 B). These are all active animals and though 

 the rostrum is close to the thorax it clearly arises from the head. Here 

 belong the cicadas, frog hoppers, tree hoppers, and leaf hoppers. 



Cicada septendecim is an example with a life cycle which may last 

 as long as seventeen years. Eggs are deposited in holes in the twigs 

 of trees. From here the newly hatched nymphs fall to the ground, into 

 which they burrow to feed on the tree roots. A stage resembling the 

 pupa of holometabolous insects is passed through before final 

 emergence. 



The second tribe is known as the Steniorhyncha. In these forms the 

 rostrum appears to arise from between the fore limbs. The antennae 



