466 
NORTH AMERICAN PLECOPTERA 
one may function as a probe for opening up the vagina of the 
female. Whether it be a probe or some other intromittent 
organ, there is present, presumably, a true penis, directly con- 
nected with the sperm ducts, for the transference of the sperma- 
tozoa. 
Arcynopteryx vagans is, perhaps, most nearly related to the 
preceding genera. The inner end (fig. 50, I) is short and stout 
with its posterior dorsal aspect forked. It seems very probable 
that the bifid portion represents lateral braces (fig. 50, L. B.) in 
a more highly developed condition. The free end (fig. 50, F) is 
made up of the characteristic parts, a stout, chitinous, club- 
shaped, median stylet surrounded by a membranous sheath 
(fig. 50, M. S.) and on either side of it, a shorter bifid stylet. 
These lateral stylets (fig. 50, L. S.) are chitinous but much more 
delicate than the median one; the two tips are unlike in form, 
the inner one which is scarcely visible in a side view of the supra- 
anal plate, is somewhat thumb-shaped, and the outer, longer and 
more spine-like. Broad para-genital plates (fig. 50, P. G. P.) 
surround the free end posteriorly and laterally, these are articu- 
lated to the posterior margins of the lateral braces, and are 
joined to the inner end by bands of muscle (fig. 50, M). 
In Protarcys hradleyi the inner part (fig. 40, I) is reduced to a 
mere stub, but the lateral braces (fig. 40, L. B.) are correspond- 
ingly larger. The median stylet (fig. 40, M. S.) is shorter than 
the laterals (fig. 40, L. S.) ; it is not unlike that of Arcynopteryx 
vagans in structure, being a chitinous rod surrounded by a fleshy 
covering, which is beset with innumerable tiny teeth directed 
ventrally; the paired stylets are slender tapering rods nearly 
reaching the dorsal margins of the para-genitals. These latter 
plates are large and rather triangular in form; they have the 
usual relations to the other parts already described under Arcyn- 
opteryx vagans. 
The supra-anal plate of Megarcys signata has a very curious 
appearance. The inner end (fig. 45, I) is larger than in the pre- 
ceding forms and the lateral braces (fig. 45, L. B.) are stout; the 
greater development of this region is necessitated, perhaps, by 
the extraordinary size of the rest of the apparatus. The median 
stylet (fig. 45, M. S.) is a large, flat, triangular, chitinous plate. 
