50 ENTOMOLOGY 
parasitic Diptera, the sclerites of the thorax tend to disappear. 
Furthermore, the absence of sclerites in the prothorax is prob- 
ably due to the lack of prothoracie wings, notwithstanding the 
so-called obsolete sutures of the pronotum in grasshoppers. 
Endoskeleton.—An insect has no internal skeleton, strictly 
speaking, though the term endoskeleton is used in reference to 
certain ingrowths of the external cuticula which serve as me- 
chanical supports or as_ protections 
for some of the internal organs. 
The tentorium of the head has al- 
ready been referred to. In the 
thorax three kinds of chitinous in- 
growths may be distinguished ac- 
cording to their positions: (1) phrag- 
mas, or dorsal projections; (2) 
apodemes, lateral; (3) apophyscs, 
ventral. The phragmas (Fig. 59) 
are commonly three large plates, 
pertaining to the meso- and meta- 
thorax, and serving for the origin 
if, Or» of indirect muscles of flight in 
of Mm A . 
| Nal Lepidoptera, Diptera, Hymenoptera 
—— . 
and other strong-winged orders. The 
apodemes are comparatively small in- 
growths, occurring sometimes in all 
Transverse sections of the 
thoracic -scements of 9 beetle, ¢hree thoracic Sepiments, tmOuen sic. 
Goliathus, to show the endo- . S i" = 
skeletal processes. A, pro- ally absent in the prothorax. ‘The 
thorax; B, mesothorax; C, 
metathorax; a, a, apophyses; : : 
ad, apodeme; p, phragma— ment as a pair of conspicuous proc- 
After KoLpe. 
apophyses occur in each thoracic seg- 
esses, which either remain separate 
or else unite more or less; leaving, however, a passage for the 
ventral nerve cord. 
These endoskeletal processes serve chiefly for the origin of 
muscles concerned with the wings or legs, and are absent in 
such wingless forms as Thysanura, Pediculidee and Mal- 
lophaga. 
