ENTOMOLOGY 



FIG. 59. 



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 prothoracic 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 : ( i ) phrag- 

 mas, or dorsal projections; (2) 

 apodemeSf lateral; ,(3) apophyses, 

 ventral. The phragmas (Fig. 59) 

 are commonly three large plates, 

 pertaining to the meso- and meta- 

 thorax, and serving for the origin 

 of indirect muscles of flight in 

 Lepidoptera, Diptera, Hymenoptera 

 and other strong-winged orders. The 

 apodemes are comparatively small in- 

 growths, occurring sometimes in all 

 three thoracic segments, though usu- 

 ally absent in the prothorax. The 

 apophyses occur in each thoracic seg- 

 ment as a pair of conspicuous proc- 

 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, Pediculidge and Mal- 

 lophaga. 



Transverse sections of the 

 thoracic segments of a beetle, 

 Goliathus, to show the endo- 

 skeletal processes. A, pro- 

 thorax; B, mesothorax; C, 

 metathorax; a, a, apophyses; 

 ad, apodeme; p, phragma. 

 After KOLBE. 



