ANATOMY AND PHYSIOLOGY. 103 
voice. Still, as, without the opportunity of studying 
it in the abdomen, we should know very little of 
their respiratory system, it seems best to defer its 
consideration till we can trace its development there. 
We proceed, therefore, here to examine the external 
appendages of the thorax, the legs and wings. The 
legs of wasps are formed on the same plan as those 
of insects generally. The names of the different 
- parts have been adopted from the limbs of Vertebrata. 
First comes a short flat joint, the coxa or hip, by 
which the limb is connected to the trunk. The next 
jomt is a still smaller piece, which is let into the 
articulation, as it were, and thus gives a much greater 
extent of movement. This is the trochanter, on 
which the limb turns. The femur or thigh, which is 
so largely developed in the grasshopper and the flea, 
succeeds to this. It stands out almost horizontally 
from the body, and is probably the first in the series 
which would attract attention. Then comes the 
shank or tibia, the long straight bone which turns 
down towards the ground. The tibize of the two 
first pair of legs have only a single spine at the end 
furthest from the body, the distal end as it is called; 
while the hind pair have two of these spines: this is 
important to recollect. Otherwise they are unarmed ; 
contrasting in this particular respect with the corres- 
ponding limbs of many of the sand-wasps, which 
are clothed quite down to the feet with strong hairs 
or spines. 
The articulation between the thigh and shank 
bones is very strong. The form of the surfaces only 
allows of movement in one direction, being a hinge 
joint. The movement by which the limbs are turned 
