84 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



deferentia beyond the vesiciilae, which unite in a slender ductus ejacu- 

 latorius (Dej), and that the latter opens into the anterior end of the 

 phallic sac (Enph). There can be no question in this species that the 

 terminal sac of the exit system is an endophallic invagination from 

 the mouth of the external penis, or ectophallus (Phi). The endo- 

 phallus is everted during copulation (fig. 29 E, Pen), and in the pro- 

 tracted condition it forms the principal part of the intromittent organ. 

 The everted " penis " of Acroneuria paciUca is figured by Needham 

 and Claassen (1925), that of Acroneuria evoluta by Clark (1934). 

 Other species shown to have an eversible phallic organ include 

 Pteronarcys nohilis (Prison, 1935), Peria hastata, Perlodes signatus, 

 and Isoperla fusca (Needham and Claassen, 1925). The wide exit 

 tube of Chloroperla granvmatica and of Isopteryx tripunctata de- 

 scribed by Klapalek (1896) as the "ductus ejaculatorius " is very 

 evidently an eversible structure. An eversible endophallus, therefore, 

 is probably a characteristic feature of the families Pteronarcidae and 

 Perlidae. 



The walls of the endophallus are mostly membranous, but they 

 may contain sclerotic areas or plates, and in some forms they are pro- 

 duced into folds or are armed with a pair of long rods or hooklike 

 processes, all such structures taking an external position with the 

 eversion of the sac. The exposed rods or hooks are called " titillators " 

 by most writers, but a rodlike internal armature of the endophallus is 

 generally termed a virga (fig. 22 B, Vrg), and the name titillator 

 given to terminal processes of the ectophallus {Ttl). 



The endophallus may be a direct invagination from the anterior 

 wall of the genital chamber, as shown by Klapalek in Chloroperla 

 {Isopteryx) tripunctata, in which the long tube, designated " ductus 

 ejaculatorius " by Klapalek, opens simply by a wide mouth, from 

 which project the tips of the endophallic rods, or virgae. In other 

 Perlidae, however, an ectophallus may be present as a distinct " penis " 

 projecting into the genital chamber and containing the mouth of the 

 endophallus. An organ of this type is well shown by Walker (1922) 

 in Perla tristis as a large globular structure concealed in the genital 

 chamber above the ninth abdominal sternum. In Acroneuria arida 

 (fig. 28 I, J) the ectophallus (Phi) is a thick, conical lobe somewhat 

 constricted at its base, with an apical opening that leads into the wide 

 endophallic sac (Enph). The phallus of this species, however, is not 

 seen directly on opening the shallow genital chamber ; it is concealed 

 in a deep pocket (phallocrypt, Crpt) of the genital chamber wall, the 

 aperture of which appears at the bottom of the external cavity. The 



