STING STRUCTURE. 
77 
its sides, and following the curve extend the whole 
length from k (Fig. 34) to r, where they are attached 
to the triangular pieces (b b) of the compound levers 
composed of the pieces b and c. Along the sheath 
are seen two T-shaped rails (Fig. 35, c, d, e, g)^ or 
guides, which exactly fit into grooves of similar form in 
the lancets, and along which they slide. The lancets 
have a fine cutting edge, and are provided along their 
outer edges towards the points with ten deep re- 
trorse barbs (Fig. 35, g, d I? b). The lancets are 
capable of being protruded beyond the sheath, so as 
to increase the depth of the wound made by that in- 
strument. 
The extent to which the lancets may be projected 
is limited by the stop at p (Fig. 35, b), while the 
sheath can enter the flesh, and is assisted in doing so 
by the teeth (b b, h), until it is stopped at the point c 
by the enlarged pouch a. From p (Fig. 35, b) along 
to their points the lancets are tubular, taking the form 
e (Fig. 35, d), lying side by side, and forming a circular 
channel a (Fig. 35, D and e) between them, through 
which the poison is injected. 
A small canal extends from the central cavity in 
the lancets to the fine teeth (Fig. 35, g, b b b), so that 
the poison not only passes down the circular channel, 
and out between the points of sting, but also through 
the canal in the lancets and out between the barbs. 
The appendage p (Fig. 35, b), of which an enlarged 
view is given at Fig. 35, f, acts as a piston to force and 
a valve to regulate the flow of poison through the channel 
between the lancets, as may be better seen in Fig. 35, c, 
