20 College of Forestry. 
rough places in the bark, anchor the anterior end of the 
body and serve as the fulcrum of a lever formed by the rest 
of the body. With each elevation of the posterior end, the 
mandibles are pressed down into the burrow and brought 
into play. As he continued he gradually worked back and 
forth around the hole, entirely encircling it. 
The freedom of movement of the head .is remarkable. 
The juncture of the head and prothorax is practically a ball 
and socket joint (Figs. 1, 3, 4) which allows the greatest 
freedom of movement in ev ery direction. The rapidity and 
range of motion of the head is also no less extraordinary. 
The head can move ventr ally till the mandibles point nearly 
backward and dorsally till the mandibles extend nearly 
directly in front. Lateral movement of the head is no less 
remarkable and often this is carried so far that the greater 
part of the eye is covered by the side of the prothorax. 
The work of making the burrow proceeds rather slowly 
until the hole is deep enough so that the anterior part of the 
prothorax extends below the margin of the opening, when it 
is continued more rapidly. The function of the rugosities 
(Figs. 1, 4, 22) on the prothorax is now quite apparent. 
In working, the insect now braces the dorsum of his pro- 
thorax against the side of the opening with his fore legs in 
the hole, his middle legs braced against the surface oF the 
bark and his hind legs eripping the bark farther back or 
waving in the air (Fig. 7). The rugosities on the prothorax 
now serve as an anchorage and also as the fulerum of a 
lever, and every push exerted by the mesothoracie legs forces 
the mandibles against the opposite side of the burrow. The 
fact that the spines on the prothorax point upward and 
backward (Figs. 1, 22) are of considerable advantage, as 
they readily allow the thorax to slip down farther into the 
burrow and obtain a firmer hold, but will not allow the body 
to slip upward as long as the prothorax is pressed firmly 
against the side of the burrow. The worker still continues 
to circle around and around the burrow while working, 
thus bringing his mandibles to bear upon all sides of it. His 
position is usually nearly perpendicular to the surface 
