40 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



ventional, and when there is a well-marked anatomical separation the 

 boundary is not the same in all cases. Carcinologists usually define 

 the " thorax " as the body region composed of the eight segments 

 between the second maxillary somite (IV) and the first abdominal 

 somite {XIII), but in some cases the head includes the first of these 

 segments. The abdomen contains six somites and the telson, except 

 in one order, the Leptostraca, in which there are seven abdominal 

 somites. The genital openings of the female are situated always on 

 the sixth thoracic segment (somite X), those of the male on the 

 eighth (somite XII). In some cases the gonoducts of the male have 

 a single median opening. The female generally is provided with a 

 sperm receptacle, which may be a median pouch of the ventral integu- 

 ment of the thorax, or paired sacs at the ends of the oviducts. 



The gonads of the Malacostraca are tubular or sac-shaped organs, 

 sometimes lobed or branched, lying in the dorsal part of the thorax 

 and abdomen, or restricted to the thorax (figs. 15 G, 16 C, 17 C, 18 E). 

 In the decapods the gonads of opposite sides are generally more or 

 less united (figs. 17 C, 18 E). The germinal cells usually occupy one 

 wall of the gonad, from which the oocytes or spermatocytes are pro- 

 liferated into the lumen (fig. 15 E) ; the cells of the opposite wall 

 (NrCls) may have a nutritive function. In Anaspides, as described 

 by Smith (1909), the mesal walls of the ovaries are produced into 

 long series of diverticula, in the apices of which are located the ger- 

 marial cells, the organs thus resembling the ovaries of insects. The 

 gonoducts are either straight or coiled, and generally open directly to 

 the exterior, but in the Brachyura the oviducts end in large ectodermal 

 sperm receptacles (fig. 18 H, Spt). 



The gonopores of male Malacostraca are located typically on or 

 close to the mesal surfaces of the coxopodites of the last pereiopods 

 (thoracic appendages), though they may lie on the sternal surface 

 between the appendages (figs. 15 D, 16 A, Gprs). Usually each aper- 

 ture is situated on the extremity of a small papilla or tubular out- 

 growth of the integument (figs. 16 B, 18 D, Pen), called a penis 

 though it is not the actual intromittent organ. In some cases there is 

 a single median penis arising from the venter of the eighth thoracic 

 segment (fig. 16 D, Pen), which contains a common outlet duct re- 

 ceiving the two lateral gonoducts at its base. If direct internal insemi- 

 nation of the female from the penes, or penis, of the male takes place 

 in any of the Malacostraca it is of rare occurrence, and has not been 

 observed. With the majority of the Malacostraca the sperm (or sper- 

 matophores) are placed by the male in the oviducts or in a sperm 

 receptaculum of the female, but the organs that accomplish the intro- 



