l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



are o)i the seventh sternum, and others state that they are between 

 the seventh and eighth sterna, the fact prohably is the same in each 

 case, since the " intersegmental " membranes of the abdomen are 

 the posterior parts of the primary segments. The mesodermal oviducts 

 retain in the adult stage the primitive position of their openings 

 on the seventh venter, or between the seventh and eighth sterna, only 

 in Ephemerida. The paired female gonopores of the Ephemerida 

 are in some species widely separated, while in others they are approxi- 

 mated and open into a slight median depression of the intersegmental 

 fold. In Dermaptera, however, the lateral oviducts open into a short 

 median ectodermal pouch between the seventh and eighth abdominal 

 sterna. 



The history of the male genital ducts of insects has been less studied 

 than that of the female ducts, but according to the elaborate em- 

 bryological studies of Heymons (1890, 1895) and Wheeler (1893), 

 the mesodermal vasa deferentia in the Orthoptera are first attached 

 to the ectoderm of the ventral wall of the tenth abdominal segment. 

 Paired male gonopores are retained in Ephemerida and in some Der- 

 maptera, but they are situated on intromittent organs, or on a single 

 organ in some Dermaptera, which appear to be evaginations of the 

 ventral wall of the ninth segment. According to Palmen (1884) the 

 vasa deferentia in half-grown ephemerid larvae are attached to the 

 posterior border of the ninth abdominal venter, and the penes are 

 formed later as evaginations of the body wall at the points of attach- 

 ment of the ducts. Palmen believed that the definitive ducts opening 

 on the penes are the ends of the primitive vasa deferentia, but Wheeler 

 (1893) found in Blasturus that a considerable length of each exit 

 tube is lined by an intima which is shed during ecdysis attached to 

 the exuviae of the penis and the body wall. In Dermaptera it is gener- 

 ally conceded that the mesodermal vasa deferentia terminate in ecto- 

 dermal ejaculatory ducts. In all the higher insects the vasa deferentia 

 come together in a single, median ejaculatory duct of ectodermal origin 

 opening on the posterior part of the ninth venter. 



TJie median ducts. — In all insects but Ephemerida and male Der- 

 maptera the lateral genital ducts discharge through a median outlet 

 tube. In the male the median duct (ductus ejaculatorius) opens on the 

 posterior part of the ninth abdominal segment, usually on an evagina- 

 tion forming an intromittent organ. In the female the opening of the 

 median duct is variable ; in some insects ( Dermaptera) it is located 

 on the posterior part of the seventh abdominal segment, in others 

 on the eighth, and in still others on the ninth segment. The nature 

 of the median female duct and the relation of the median genital open- 



