396 Annals Entomological Society of America [Vol. VI, 



helps to hold the female. The penes are the intromittent 

 organs. In Hexagenia they consist of two chitinous funnels 

 whose larger ends open inside the body, and whose smaller 

 ends are slender tubes bent down ventrally. Between the 

 penes is a t^in chitinous plate, and beneath they are supported 

 by the tenth sternite. In each penis the seminal duct can 

 be clearly traced to its termination at the end of the bent tube. 

 Of the more complicated condition which exists in most 

 May-flies, the genitalia of Siphlurus alternatus is fairly typical 

 (PI. LI). The forceps are similar to those of Hexagenia. 

 Their origin from the ninth sternite is shown in Figures 48 

 and 49. The penes (P) are wholly hidden from beneath 

 by the tenth sternite, but they are attached only at their 

 bases, and in copulation may be freely projected within the 

 (Fig. 50, EV) egg valve, while the tenth sternite remains 

 outside it. Essentially they consist of the funnels just de- 

 scribed in Hexagenia with secondary structures added. Th6 

 larger ends of the funnels open into the body (Fig. 49, A). 

 In Figure 49 the penes are shown in dorsal view, separated off 

 from the dorsal part of the abdomen with the large ends of 

 the funnels exposed (A). The small end of the funnel (B) 

 extends outside the body and turns downward as in Hexagenia, 

 but the opening of the seminal duct is enlarged and trumpet- 

 shaped. From the dorsal side only the backs of these trumpets 

 can be seen, but when the penes are completely removed 

 from the ninth sternite and turned with their ventral sides 

 up, one can look directly down into their openings, (Fig. 52, O. 

 S. D.) and the seminal ducts can be traced from the testes 

 directly to them. Lying dorsal and lateral to each seminal 

 tube are two prominent, heavy chitinized processes (Fig. 49). 

 The raised apex of the upper process (C) is pointed toward 

 the middle, that of the lower (D) is pointed outward toward 

 the side and the prominent spines upon each are directed in 

 different directions. If the supposed position of the penes 

 in copulation, be correct, the dorsal or spinose surface of these 

 processes must be in contact with the inner surface of the egg 

 valve (E. V. Fig. 50). When inserted they would thus hook 

 over its soft lip and pull it down, allowing the seminal tubes 

 to discharge their contents at the mouth of the oviducts. 



