162 



TEXT-BOOK OF ENTOMOLOGY 



tin- tun tergites; 1-9, the nine urites ; c, 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. 1 7(1 ). 

 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 pleural 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 Panorpidee 

 (Fig. 177), Diptera, and 

 aculeate Hymenoptera; 

 in the Chrysididse 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- 

 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 



FIG. 177. End of abdomen of Piumr/xt <l, l>ili dnixvn out, 

 the cliitinous pirrc- >h;ulr<l : /,, lateral, L>, dorsal view : c, 

 jointed em-opoda. <;isslcr <tfl. 



