LIBRARY

20 COLLEGE ENTOMOLOGY
des of the legs and wings. The great specialization that takes lllace in the
thorax is due to the development of muscle tissue.
Regions. - In most adult insects three thoracic regions arc discernible:
Prothorax - the anterior arihromere which is exceedingly variable in size
and shape, being very greatly reduced in certain species and very greatly
lengthened in others; it bears the forelegs and frequently a pair of spiracles.
Mesothorax - t.he median arthromere which is normally enlarged
rna
FIG. 11. Head and sucking l110uth parts of the grape lcufhopper. ErylhronsZlra comes (Say).
(Frolb Insects of Western North America.)
and muscular and beclrs the large fore pair of wings and the middle legs.
Metathorax - the POsterior arthromere; somewhat smaller than the mesothorax;
bearing the hind pair of wings and the longer and often larger hind
pair of legs.
Sclerites and intersegmehtal plates of the thorax:
Tergites - the tergum is usually a siml11e undivided dorsal sc1erite or
notum. Thus in the i;horax there are the pronotum, mesonotum, and metanotum.
The notum lnay appear as two smaller sc1erites, the scutum and
the postnotum or postscutellum, or as three sclerites, the prescutum, scutum,
scutellum. The paiagia are flat lobe-like or stalked structures produced
latterally and backwCirds from the pronotum in mosquitoes, moths, and
butterflies, and the Po.rapsides result from the division of the scutum of the
mesonotum into two parts in chalcid flies.
Pleurites or the lateral, usually oblique, sclerites are separated by the pleural'
suture into two main divisions: (1) Episternum or anterior larger sclerite
which may in certain tases be demarked into preepisternum. a se ledte ante-