ANATOMY AND PHYSIOLOGY 



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FIG. 76. 



abdominal mass, the remaining segments being reduced and 

 inconspicuous. The terminal segments of the abdomen often 

 telescope into one another, as in 

 many Coleoptera and Hymenop- 

 tera (Chrysididae), or undergo 

 other modifications of form and 

 position which obscure the seg- 

 mentation. As to the number of 

 evident (not actual) abdominal 

 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 Hymenop- 

 tera, nine (Tenthredinidae) or as 

 few as three (Chrysididae). In 

 the larvae of these insects, how- 

 ever, nine or ten abdominal seg- 

 ments are usually distinguishable, 

 though the tenth is frequently 

 modified, being in caterpillars 

 united with the ninth. 

 Appendages. Rudimentary ab- 

 dominal limbs occur in Thysanura 

 (Machilis, Fig. 76). Functional 

 abdominal legs do not occur in 

 adult insects, but in larvae the ab- 

 dominal pro-lqgs (often called " false legs," Fig. 64) are ho- 

 mologous with the thoracic legs and the other paired segmental 

 appendages, as the embryology shows. The embryo of (Ecan- 

 thus, according to Ayers, has ten pairs of abdominal appen- 

 dages (Fig. 196), 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 



Ventral aspect of the abdomen 

 of a female Machilis maritima, to 

 show rudimentary limbs (a) of 

 segments two to nine. (The left 

 appendage of the ninth segment is 

 omitted.) c, c, c, cerci. After 

 OUDEMANS. 



