OR INSECT OF ITCH AND MANGE. 
375 
the middle that the two spears can be distinguished. It can 
also lift up these projections, or separate them from the trunk, 
and, when they are replaced, they lie on the trunk in the same 
manner as one jaw bone lies on the other. 
Lastly, the animal has the power of protruding these spears 
either separately or together, and of withdrawing them again. 
When the spears are pushed forward to their utmost extent, they 
project beyond the trunk about a third part of the length of the 
head ; and when quite drawn in, they lie under the upper skin of 
the head. As this skin is rather transparent, the opaque spears 
can be seen through it-when they are drawn in, like two black 
lines situated close by one another. 
When an acarus cannot easily get away from the place where 
he is (for instance, his legs are entangled with the legs of another 
mite), then we can clearly see the protrusion and retraction of 
these spears. This can also be caused by pressing the head of 
one of these animals between two plates of glass. When the 
animal is thus compressed, we can frequently, but not always, 
see a hair-like substance protruded between the trunk and the 
spears, about the same length as the latter, but half of it is 
thinner than them. The use of this part I do not know. 
Near to where the spears are fixed, and on each side of them, 
is found a short fine stiff hair, the point of which is directed 
forwards and outwards ; and rather above, and further out, is 
placed a second and shorter hair. Above these last mentioned 
hairs is seen on each side of the head, near to the edge, a 
rounded prominent and transparent spot, surrounded by a dark 
line. These spots have been supposed to be the eyes. 
At a short space behind the eyes, the upper part of the head 
appears to be much thicker than at the front. The head is 
liere united to the thick part of the throat, and can only be 
distinguished from it by its motions, which take place in all 
directions, and especially downwards. On the under side of the 
throat, shortly before it begins to be concealed under the coat of 
mail of the trunk, are seen a number of dark red spots near to 
one another, but at irregular distances. 
The four fore feet {hhhb) are ranged two on each side of the 
body near to the head, directed forwards and a little outwards. 
They are throughout of equal form and consistence, their length 
generally agrees with the breadth of the body, and is about dou¬ 
ble the length of the whole head. Their thickness near to the 
body is about two-thirds of that of the head at its thickest 
part; it diminishes, however, towards the outer end so much 
as to appear almost pointed. Each foot is furnished with four 
joints easily distinguishable. The first of these, that is the one 
