THE THORAX. 



613 



running Orthoptera, but in insects whose flight is powerful they 

 are closely fused together and it is difficult to analyse the thorax 

 into its component parts (Fig. 335). In such insects the terga 

 of the meso- and meta- thorax, or mesonotum and metanotum as 

 they are called, may each be divided into as many as four areas 

 called the praescutum, scutum, scutellum and postscutellum 

 respectively. The pleuron in each of the three segments 

 is usually divided into an episternum and an epimeron ; and to 

 these with the sterna the three pairs of legs are attached. A 

 pair of lobes or sausage-shaped projections, termed patagia, 

 lie on each side of the prothorax in Diptera and Lepidoptera. 

 They give origin to the attachment of certain muscles in the 

 Culicidae. A somewhat similar pair of processes, the tegulae, on 

 the meso-thorax overlying the base of the fore- wings in Lepidop- 

 tera and certain Hymenoptera are sometimes, but probably on 



Sc 



FIG. 336. Th3 right wing of a male Anopheles mvculipennis Meigen x about 14 (from Nuttall 

 and Shipley). The scales have been removed to show the nervuration. The nervures 

 and cells are named after the plan of Comstock and Needham. A anal area ; 1st A anal 

 nervure ; C costa ; Cu cubitus ; H humeral cross-nervure ; I cross-nervure between R% 

 and #4 + 5; J cross-nervure between radial and medial systems ; K cross-nervure between 

 medial and cubital systems ; M media ; cross-nervure between HI and RZ ; jR radius 

 Sc subcosta. 



insufficient grounds, homologized with the wings. In the higher 

 members of the latter group the first abdominal segment becomes, 

 in the imago, so fused with the thorax as to seem to belong to 

 this region. A curiously complicated skeleton of apodemes or 

 processes for the attachment of muscles is often present in the 

 thorax ; it varies much in different insects. 



The wings are confined to the meso- and meta-thorax and in 

 the great majority of cases both pairs are present. If one pair 

 only exists it is almost always the meso-thoracic and in one 

 large class the Diptera the meta-thoracic wings are replaced by 

 the so-called halter es * or balancers. Many of the more primitive 



* 01 d\T77pes = dumb-bells used in jumping. 



