132 ' WHEELER. [Vol. VIII. 



have independent openings. The oviducts open at the posterior 

 edge of the seventh, the deferent ducts, which are continued 

 into a pair of penes, at the posterior edge of the ninth segment. 

 There is no ductus ejaculatorius proper since, according to 

 Palmen, the chitinous cuticula covering the surface of the body 

 does not extend in beyond the lips of the orifices.^ In the 

 females of Hcptagenia the oviducts open at the bottom of an 

 infolding of the hypodermis between the seventh and eighth 

 segments. This infolding, the ovivalvula, accommodates the 

 mature eggs till the time for oviposition, and may be regarded 

 as a structure on the way to becoming a vagina. Morphologi- 

 cally it is simply an intersegmental depression differing from 

 those which separate the sternites of other segments only in 

 being somewhat exaggerated. Palmen observed that the male 

 genital ostia are not opened till the last nymphal ecdysis. 



A comparison of the nymphal Ephemerid with the Ortho- 

 pteran embryo is very instructive. In Xiphidiiun and Blatta the 

 female ampullae lie at the hind end of the seventh, the male at 

 the hind end of the ninth abdominal segment. Just as the 

 deferent ducts of Ephemerids extend into the penes and open to 

 the exterior, so the terminal ampullae originally extend into a 

 pair of appendages, albeit on the tenth segment and not opening 

 to the exterior. If the penes of Ephemerids are really modified 

 ambulatory appendages they would be homologous with the 

 styli of Orthoptera. The curious persistence of these append- 

 ages in existing Orthoptera may be due to their having once 

 functioned as penes, long after the other abdominal ambulatory 

 appendages had disappeared. It would be necessary to suppose, 

 if this view were adopted, that the terminations of the male 

 ducts had moved backwards. But this whole matter is very 



1 Palmen claims ('84, p. 82) to have found no chitinous lining in the terminal 

 portion of the ejaculatory ducts and oviducts of Ephemerids — an observation 

 from which he naturally infers that these ducts are mesodermal throughout their 

 entire length. I have found, however, that there is in the nymph of a species of 

 Blasttiriis very common in the ponds of Worcester, Mass., a distinct chitinous 

 lining to the ejaculatory ducts for some distance inward from the orifice of either 

 penis. My attention was attracted to this lining during the ecdysis of the insect, 

 when I saw the membrane withdrawn from the ducts along with the cuticle 

 covering the external surfaces of the penes and terminal abdominal segments. 



