\\ \ rOMV AND PHYS >.s 





a 



the l>a>e of the abdomen in relation to the thorax. Inn >v to 



modifications .!' the extremity <>f the abdomen, for -exual purposes. 

 Modifications. In aculeate Il\ inenoptera the lir-t Segment aA 

 abdomen has been transferred to the thorax, where it 

 propodcHtu, or median segment; in other words, what appear- to i 

 lirM abdominal segment is actually the second; this, U in bee- 

 wasps, often forms a petiole, which enable- 

 the sting to be applied in almost any din 

 tion. In Cynipida- the tergum of segment 

 two or three occupies most of the abdom- 

 inal mass, the remaining segments being 

 reduced and inconspicuous. The terminal 

 segments of the abdomen often telescope 

 into one another, as in many Coleoptera and 

 Ilymeiioptera (Chrysididae), or undergo 

 other modifications of form and position 

 which obscure the segmentation. As to 

 the number of evident (not actual) abdom- 

 inal segments, Coleoptera show five or six 

 ventrally and seven , or eight dorsally; 

 Lepidoptera, seven in the female and eight 

 in the male; Diptera, nine (male Tipulidae) 

 or only four or five; and Hymenoptera, nine 

 (Tenthredinidae) or as few as three (Chry- 

 sididae). In the larvae of these insects, 

 nine or ten abdominal segments are usually 

 distinguishable, though the tenth is fre- 

 quently modified, being in caterpillars 



United with the ninth. FIG. 78. Ventral aspect of the 



_, .. . . . . abdomen of a female Machilis 



Appendages. Rudimentary abdominal ma ritima, to show rudimentary 

 limbs occur in Thysanura (Machilis, Fig. l ^^ t ap^SS^Vfthe eighTh 



78) . Functional abdominal legs do not OCCUr segment is omitted.) c, c, c. lateral 

 j 1 , i_ .. i AI_ i_j cerci and median pseudocercus. 



in adult insects, but in larvae the abdom- Mter QUDEMANS. 

 inal rolegs (Fig. 66) are homologous 



with the thoracic legs and the other paired segmental appendages, as 

 the embryology shows. The embryo of (Ecanthus, according to Ayers, 

 has ten pairs of abdominal appendages (Fig. 199), equivalent to the 

 thoracic legs. Most of these embryonic abdominal appendages are 

 only transitory, but the last three pairs frequently persist to form the 

 genitalia, as in Orthoptera (to which order (Ecanthus belongs". In 



