Smithsonian miscellaneous collections . s a groove on its upper surface that leads into adeep cavity at the base of the lobe. The second gonopods (E) havemore nearly the structure of the unmodified pleopods of the follow-ing segments. Each is a biramous appendage with the two arms{Expd, Endpd) supported on a two-segmented basal stalk {Cxpd,iTr). The larger endopodite bears a mesal lobe {d) at the end ofits long first segment, which, when the appendage is turned forwardbeneath the corresponding first gonopod, clasps the latter at the baseof its mesal lobe. The structure of the crayfish gonopods
Smithsonian miscellaneous collections . s a groove on its upper surface that leads into adeep cavity at the base of the lobe. The second gonopods (E) havemore nearly the structure of the unmodified pleopods of the follow-ing segments. Each is a biramous appendage with the two arms{Expd, Endpd) supported on a two-segmented basal stalk {Cxpd,iTr). The larger endopodite bears a mesal lobe {d) at the end ofits long first segment, which, when the appendage is turned forwardbeneath the corresponding first gonopod, clasps the latter at the baseof its mesal lobe. The structure of the crayfish gonopods and themanner in which the appendages perform their function of spermintromission during copulation are minutely described for CambarusaMnis by Andrews (1911). The spermatozoa are received from the NO. 14 INSECT ABDOMEN SNODGRASS 45 penes into the grooves of the mesal lobes and the pockets at their baseson the first gonopods, and are discharged into a receptacular pouch(annuhis ventralis) on the venter of the female between the sterna. FiG. 17.—Crustacea-Malacostraca-Eucarida: male genitalia of a crayfish,Caml)a<nis virilis. A, posterior view of lower part of last thoracic segment, showing small penesprojecting mesally from coxopodites. B, first gonopods projecting forward,anterior (upper) surface. C, testes and vasa deferentia, dorsal view. -D, firstgonopods (normally projecting forward in ventral channel of thorax), posterior(under) surface. E, second gonopods, posterior (under) surface. a, distal shaft of first gonopod; b, c, outer and inner branches of ventral lobeof first gonopod; Cxpd, coxopodite; d, distal lobe of second gonopod; Dej, ductusejaculatorius ; Endpd, endopodite; Expd, exopodite; Gpr, gonopore; Pen, penis ;PI, pleuron; Stn, sternum; T, tergum; Tes, testis; iTr, first trochanter (basip-odite) ; Vd, vas deferens. of the seventh and eighth thoracic segments. (See also Andrews,1906.) The crabs (Brachyura) dififer from most of the other decapodsin that the f
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