TEXT-BOOK OF ENTOMOLOGY 



form the base of attachment. The scutum is invariably present, as 



is the scutellum. The former in nearly all insects constitutes the 



larger part of the tergum, while the latter is, as its name implies, the 



small shield-shaped piece 

 directly behind the scutum. 

 The praescutum and post- 

 scutellurn are usually mi- 

 nute and crowded down out 

 of sight between the oppos- 

 ing segments. As seen in 

 Fig. 90, the prsescutum of 

 most moths (Telea) is a 

 small rounded piece, bent 

 vertically down so as not 

 to be seen from above. In 

 Polystoechotes and also in 

 Hepialus the praescutum is 

 large, well-developed, tri- 

 angular, and wedged in 

 between the two halves of 



the scutum. The postscutellum is still smaller, usually forming a 



transverse ridge, and is rarely used in taxonomy. 



The metathorax is usually smaller and shorter than the mesotho- 



rax, being proportioned to 



the size of the wings. In 



certain Neuroptera and in 



Hepialidae and some tin- 



eoid moths, where the 



hind wings are nearly as 



large as those of the 



anterior pair, the meta- 

 thorax is more than half 



or nearly two-thirds as 



large as the rnesothorax. 



In Hepialidse the prsescu- 



FIG. 90. Thorax of Telea polyphemun, side view, 

 pronotum not represented : em, epimerum of prothorax, 

 the narrow piece above being the prothoracic episternum; 

 ms, mesoscutuin ; #cm, mesoscutellum ; ms", inetas- 

 cuturu ; scm'", metascutellum ; pt, a supplementary 

 piece near the insertion of tegulae ; w, pieces situated at 

 the insertion of the wings, and surrounded by mem- 

 brane ; epm", episternum of the mesothorax ; em", 

 epimerum of the same; epm"', episternuin of the 

 metathorax; em'", epimerum of the same, divided into 

 two pieces; o', c", c'", coxae; te', te", te'", trochan- 

 tines ; tr, tr, tr, trochanters. A, tergal view of the 

 mesothorax of the same ; prtn, prsescutum ; me, scu- 

 tum ; scm, scutellum ; ptm, postscutellum ; t, tegula. 



turn is large and distinct, 

 while the scutum is di- 

 vided into two widely 



FIG. 91. Thorax of the house-fly: prn, pronotum; 

 }/>:. praescutum ; no' , mesoscutum : set', mesoscutellum ; 

 pxcl', jiostscutellum ; al, insertion of squama, extending 

 to the insertion of the wings, which have been it-moved ; 

 iiixjilii', mesophragma ; h, balancer (halter); pt, tegula; 

 mtn, metanotum ; <///*, <///'. </</*", epiMenium of ]>n>-, 

 meso-, and meta-thorax ; t-jnn'. </<///". im-so- and meta- 

 epimerum ; gt', at", meso- and meta- stern um ; car', ex", 

 car'", coxae; tr'. tr", tr'", trochanters of the three pairs 

 of legs; M/I', x/i", */'"'. #p"", sp'"", first to fifth spir- 

 acles; tg , .t</", tergites of first and second abdominal 

 segments; u , u", urites. 



separated pieces. The 

 postscutellum is nearly or quite obsolete. 



The pleurum in each of the three thoracic segments is divided 

 into two pieces ; the one in front is called the episternum) since it 



