ORGANS FOR SPERM-TRANSFER 267 
bony ridge much thicker than the ulna plate from which it is 
faintly marked off by a suture. Thus in sections (fig. 8), the 
radius looks like a head on a slender neck. The abrupt termina- 
tion of the radius is very like the elbow end of the human radius, 
a shallow cup. The actual cup is made by clear horny matter of 
considerable thickness and is prolonged as a horny sharp ridge all 
along the radial edge of the pyramidal wedge. The head of the 
radius stands out as wider than the neck (fig. vir). 
The ulna is but a vaguely defined thick area of the general 
shell and it continues as the hand or wedge, which is, next to the 
head of the radius, the most peculiar part of the triangle. This 
wedge is a hard horny pyramid of three faces. One is rounded 
and setose, two flat, meeting at a sharp edge, (see small sketch, 
fig. 22). Its exposed rounded face (figs. v1, vi1) is set with a dense 
brush of plumose setae. The external or ulnar face (fig. vi) is 
smooth bone, bearing setae along its right edge and ending, to the 
left, in the sharp horny ridge that runs up from the head of the 
radius and is shown as a dark shade in fig. v. The concealed 
innermost face is bony and contains orange pigment; along its 
left edge it bears setae (fig. vim), and its right edge is thesharp 
horny membrane that runs up from the head of the radius. In 
the union of this face with the soft membrane of the concavity of 
the triangle there is a bony articular plate. 
The photographs donot represent one feature of the triangle and 
that is the small tuft of some five or six, or so, very wiry bent 
plumose setae that spring from the elbow of the triangle and, for 
the most part, curve so as to lie down close to the soft membrane. 
These setae are roughly shown in fig. 22 at the elbow. This also 
gives in the side sketch, an end view of the head of the radius as 
seen when the base of the wedge was cut off and the stump of the 
ulna and free end of the radius viewed from the face where the 
wedge had been. This is intended to show the head of the radius 
as a rounded saucer with flat bottom, not deep, but with flaring 
and rounded sides that form a rim thicker than the neck of the 
radius below. The cut off setae in this figure are the bases of those 
on the union of ulna and wedge, just above the level of the line 
23 in the main fig. 22. 
