162 



TEXT-BOOK OF ENTOMOLOGY 



Fin. 17i>. Abdomen of Termesfiavipes : 1-10, 

 the ten tergites ; 1-9, the nine urites ; o, cercopod. 



THE ABDOMEN AND ITS APPENDAGES 



In the abdomen the segments are more equally developed than 



elsewhere, retaining the simple annular shape of embryonic life, 



and from their generalized 

 nature their number can be 

 readily distinguished (Fig. 176). 

 The tergal and sternal pieces of 

 each segment are of nearly the 

 same size, the tergal often over- 

 lapping the sternal (though in 

 the Coleoptera the sternites are 



larger than the tergites), while there are no pleura! pieces, the 



lateral region being membranous when visible and bearing the 



stigmata (Fig. 177, L). In the terminal segments beyond the genital 



outlet, however, there 



is a reduction in and 



loss of segments, espe- 

 cially in the adults of 



the metabolous orders, 



notably the Panorpidse 



(Fig. 177), Diptera, and 



aculeate Hymenoptera; 



in the Chrysididae only 



three or four being 



usually visible, the 



distal segments being 



reduced and telescoped 



inward. 



The typical number 



of abdominal segments 



(uromeres), i.e. that 



occurring in each order 



of insects, is ten ; and 



in certain families of 



Orthoptera, eleven. In 



the embryos, however, 



of the most general- 



i" 



c 



Fin. 177. End of abdomen of Panorpn ih'hilix drawn out. 

 the chitinous pirn's shaded : /,, lateral, 1>, dorsal view ; <. 

 jointed eeivopoda. (Ussier del. 



ized winged orders, Orthoptera (Fig. 199), Dermaptera, and Odonata, 

 eleven can be seen, while Heymons has recently detected twelve 

 in blattid and Forficula embryos, and he claims that in the nymphs 

 of certain Odonata there are twelve segments, the twelfth being 



