58 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



95 



insects opened originally on segment XVII, which is the tenth abdomi- 

 nal segment (fig. 21 A, Vd), and that very probably the gonopores 

 were located on the bases of the segmental appendages, as is the case 

 in many other arthropods. The usual common exit duct, ductus ejacu- 

 latorius (B, Dej), is formed ontogenetically as a median invagina- 

 tion at the posterior margin of the venter of the ninth abdominal 

 segment. Anatomically the point of origin of the ejaculatory duct 



XVII 



xvin 



Fig. 21. — Diagrams showing tlie relation of the male genital ducts in Orthoptera 

 to the nerves of the tenth and eleventh abdominal segments. 



A, primitive stage: vasa deferentia (Vd) opening separately on tenth abdomi- 

 nal segment (postoral somite XVII) between the lateral nerves of tenth and 

 eleventh segments. B, later stage : vasa deferentia opening medially into an 

 ejaculatory duct {Dcj) invaginated at posterior end of ninth abdominal segment ; 

 last three ganglia of nerve cord moved forward, drawing the cereal nerves 

 (CerNv) over the genital ducts. C, definitive stage: the last four ganglia united 

 in eighth abdominal segment ; genital exit system extended forward by growth 

 of ejaculatory duct and addition of genital chamber (GC), the vasa deferentia 

 looped beneath the cereal nerves. 



Ab, abdominal segments; AcGld, accessory genital gland; Ccr, cercus; CerNv, 

 cereal nerve: Dcj, ductus ejaculatorius ; GC, genital chamber; Tes, testis; Vd, 

 vas deferens; VI-XI (on right), abdominal segments; XIII-XVIII (on left), 

 postoral somites. 



appears thus to be interseginental between the ninth and tenth abdomi- 

 nal segments, but some incompleted observations made by the writer 

 on the innervation of the genital organs in Orthoptera seem to indi- 

 cate that the ductus ejaculatorius derives its innervation from nerve 

 trunks that pertain to the tenth segment. It is possible, therefore, that 

 the median genital duct of the male morphologically belongs to the 

 tenth abdominal somite. Perhaps the median duct was primarily the 

 outlet of the accessory genital glands (B, AcGld), but, whatever its 



