68 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



apparently single genital segment of the adult may be a mere mem- 

 branous ring (A, GSeg), or it may be a well-developed segment with 

 dorsal and ventral plates (C, gT, gS). In Lithobius the ventral plate 

 of the genital segment bears laterally on its posterior margin a pair of 

 small, three-segmented appendages, the gonopods (B, C, Gp, E), the 

 basal muscles of which (E, O, Q) arise on the sternal plate of the 

 segment. The definitive sternum of the genital segment, theijefore, is 

 clearly a composite plate which includes the true bases of the genital 

 appendages united with the primitive segmental sternum. The free 

 genital appendages, then, are not the entire gonopods, but are the 

 telopodites of the latter, and their muscles (E, O, Q) are the levators 

 and depressors of the first trochanter (Tr). 



In the males of many insects of the higher orders the structure of 

 the second genital segment and its clasperlike appendages (the harpes) 

 closely resembles the condition in Lithobius. Though the claspers are 

 but one-segmented, they are movable by muscles arising in the gonopod 

 bases, and the latter are generally more or less united with the sternum. 

 In the insects, however, it is not so clear that the claspers are the true 

 telopodites of the gonopods, since there is evidence to suggest that 

 they may be other appendicular processes of the bases of the genital 

 appendages. 



ABDOMINAL APPENDAGES OF CRUSTACEA 



All the body segments of the Crustacea anterior to the telson are 

 usually provided with well-developed appendages. In the lower crus- 

 tacean groups, the appendages of the entire body series, as in Apus 

 (fig. 28 A), are fundamentally uniramous in form, though the various 

 segments may be provided with endite and exite lobes. Each limb 

 consists of a basis (LB), called the coxopodite, and of a telopodite 

 (Tlpd). The frequent biramous form of crustacean appendages (C) 

 is evidently the result of the hyper-development of an exite of the 

 basal segment of the telopodite (the first trochanter, or basipodite, 

 Bspd). The shaft of the telopodite beyond the basipodite then be- 

 comes the endopodite (Endpd). The exite lobes are movable by mus- 

 cles arising in the limb segments that support them. 



The abdominal appendages of the Malacostraca are typically bira- 

 mous limbs (fig. 28 C) in which the endopodite (Endpd) is usually 

 reduced to the size of the exopodite (Expd). The basis, or coxopodite 

 (Cxpd), and the basipodite (Bspd) may be distinct segments, but in 

 some forms (B) they are united in a single protopodite (Prtpd). 

 In certain cases the abdominal appendages become practically unira- 



