48 ENTOMOLOGY 
tinct pieces, or sclerites, as represented diagrammatically in 
Fig. 56. Thus the tergum of a wing-bearing segment is re- 
garded as being composed of four sclerites (tergites, Fig. 57), 
namely and in order, prescutum, scutum, scutellum and post- 
scutellum. The scutum and scutellum are commonly evident, 
but the two other sclerites are 
Fic. 57. 
usually small and may be absent. 
Fach pleuron consists chiefly of 
two sclerites (pleurites, Fig. 58), 
separated from each other by a 
more or less oblique — suture. 
The anterior of these two, which 
joins the sternum, is termed the 
episternum,; the other, the epi- 
meron. The former is divided 
into two sclerites in Odonata and 
both are so divided in Neuroptera. 
The sternum, though usually 
a single plate, is in some in- 
stances divided into halves, as 
Sena oe Se in the cockroach, or even into 
2, mesoprescutum; 3, mesoscutum; 4 five sclerites (Forficulide ). 
To these should be added the 
mesoscutellum; 5, mesopostscutellum; 
a pair 
6, metaprescutum; 7, metascutum, 8, 
metascutellum; 9, metapostscutellum. aah: c = 2 # 
patagia of Lepidoptera 
—After Newport. ; 
of erectile appendages of the 
prothorax; and the paraptera, or tegule, of Lepidoptera and 
a pair of small sclerites at the bases of the 
lymenoptera 
front wings. 
Each thoracic segment bears a pair of spiracles in the em- 
bryo and in some adults as well (Campodea, Heteroptera), 
but in most imagines there are only two pairs of thoracic 
spiracles, the suppressed pair being usually the prothoracic. 
The sclerites of the thorax owe their origin probably to 
local strains on the integument, brought about by the muscles 
of the thorax. Thus the primitively wingless Thysanura and 
Collembola have no hard thoracic sclerites, though certain 
