14 Annals Entomological Society of America [Vol. XV, 



into a huge spout-like organ, which is bent upwards and forwards 

 over the terga of the ninth and tenth segments. This structure 

 (spc) consists of a tubular process with a spear-shaped extremity 

 and rests in another more flattened trough-like piece. The two 

 are received into a mid-dorsal groove on segments 9 and 10 

 and their free extremities are apparently received into a notch 

 under cover of the elevated and slightly produced edge of the 

 8th tergum. If we examine the ventral surface of this peculiar 

 structure, which is evidently a sperm-conveyor, we see that its 

 base is marked ofi^ from the rest of the supra-anal plate by a 

 transverse suture, under the edge of which is the proximal 

 opening into the lumen of the sperm-conveyor. Leading from 

 the opening of the ejaculatory duct is a groove with thickened 

 sides, which passes between the flat paraprocts and along the 

 ventral surface of the supra-anal plate, to the opening of the 

 sperm-conveyor. This is evidently a seminal groove, along 

 which the spermatic fluid is conducted from the ejaculatory 

 duct into the sperm-conveyor through the proximal opening 

 of the latter. There is no true penis in this species. 



In the Pteronarcinee and some, at least, of the Perlinas 

 (Perlodini) there is a somewhat similar modification of the 

 supra-anal plate, differing from that of Capnia, however, in 

 that the median part is deeply invaginated into a pocket, so 

 that there is no prominent, projecting external structure. 

 In some species of Pteroiiarcys, according to Smith ('17), this 

 structure serves as a sperm-conveyor, while in others it is 

 apparently modified for another function, that of a "probe-like 

 organ in opening up the genital passages of the female." In 

 the Perlodini its function is generally, if not always, more of the 

 latter nature, serving apparently as a titillator or copulatory 

 hook. In both groups the structure is similar enough to indicate 

 a common origin. 



In Isogenus frontalis Newm. (PI. II, Figs. 14-17), which 

 I have taken as an example of this type, there is a deep, narrow, 

 median invagination of the tenth tergal region, as well as the 

 supra-anal plate. The tenth tergum is thus divided into 

 two " hemi-tergites, " each of which is somewhat thickened at 

 its mesocaudal angle, where it bears a few denticles. In other 

 species of this group these angles may be raised into hook-like 

 projections (e. g., Arcynopteryx americana, Klapalek, op. cit.) 

 The invaginated part of the tenth tergum forms a large median 



