INTRODUCTION. 7 
The lower lip and the jaws carry on the outside certain nervous 
filaments which have received the name of palpi. 
When speaking of sucking insects, and in general of the various 
orders of insects, we shall speak more in detail of the various 
parts of the mouth. 
The thorax (Fig. 6), the second primary division of the body 
of insects, plays almost as important a part as the head. It con- 
sists of three segments or rings, 
the prothorax, the mesothorax, 
and the metathorax, each of 
which bears a pair of legs, and 
they are in general joined to- 3 
gether. The wings are attached Fig! atoms of Acrotinus lonpiidanna 
to the two posterior segments. Sa iar 
All insects have six legs. There is no exception whatever to 
this rule, though some may not be developed. 
After the segments to which they are attached the legs are 
called anterior, posterior, and intermediate. The legs are com- 
posed of four parts: the trochanter, a short joint which unites the 
thigh to the body, the thigh or femur, the tibia, answering to the 
shank in animals, and the tarsus, or foot, composed of a variable 
number of pieces placed end to 
end and called the phalanges. 
We take for example the 
front leg of a AHeterocerus 
(Fig. 7), and the posterior leg 
of a Zophosis (Fig. 8), genera 
of beetles. 
We shall not dwell on the 
different parts, as they perform 
functions which will occupy us 
later, when speaking of the 
various species of the great 




class of insects. Fig. 7.—Hind leg of a Fig. 8.—Front leg 
The functions which the  e!rocerus. Se 
legs of insects have to perform consist in walking, swimming, or 
jumping. 
In walking, says M. Lacordaire, insects move their legs 

