48 DEFINITION OF THE TERM INSECT. 
the expense of others, and a variation in form takes place, 
none, as M. Savigny has elaborately proved, are totally 
obliterated or without some representative*. The organs 
now described, except the upper lip, are formed after 
a quite different type from those of Vertebrata, with which 
they agree only in their oral situation and use. 
The second portion of the body is the Trunk, which 
is interposed between the head and abdomen, and in 
most insects consists of three principal segments, sub- 
divided into several pieces, which I shall afterwards ex- 
plain to you. I shall only observe, that some slight ana- 
logy may perhaps be traced between these pieces and the 
vertebree and ribs of vertebrate animals, particularly the 
Chelonian reptiles. This is most observable in the Locus- 
tina, &c. and Libellulina, in which the lateral pieces of 
the trunk are parallel to each other®. In the Diptera and 
many of the Aptera most of these pieces are not separated 
by sutures. Each of the segments into which the trunk is 
resolvable bears a pair of jointed legs, the first pair point- 
ing to the head, and the two last to the anus. These legs 
in their composition bear a considerable analogy to those 
of quadrupeds, &c., consisting of hip, thigh, leg, and 
foot; but the last of these, the foot or Tarsus, is almost 
universally monodactyle, unless we regard the Calcaria 
that arm the end of the tibia, as representing fingers or 
toes, an idea which their use seems to justify. Gryllus 
monstrosus and Tridactylus paradoxus, however ©, exhibit 
some appearance of a phalanx of these organs. They 
differ from them first in number, the thoracic legs being 
* Anim. sans Vertebr. I. i. Mem. i. 
b Prate VIII. Fic. 10—14; IX. Fic. 6—8. 
* Coquebert Ilust. Ic. iii. t, xxi. fi 3. 
