DEFINITION OF THE TERM INSECT. 49 
invariably s¢v in all insects, with the exception of the 
Octopods or most of the Trachean Arachnida, which have 
usually eght. In the Myriapods, though there are hun- 
dreds of abdominal legs, only six are affixed to the trunk. 
Next they differ with regard to the sztuation of their legs ; 
for though the anterior pair or arms are analogous in 
that respect, the posterior pair are not, sce in guadru- 
peds these legs are placed behind the abdomen, but in 
insects before it—in fact, in the former the legs may be 
considered as placed at each end of the body, excluding 
only the head and tail, but in the latter in the middle. 
Though they correspond with those of quadrupeds in 
being in paz7s or opposite to each other, yet their direc- 
tion with respect to the body is different, the legs of 
quadrupeds, &c. being nearly straight, whereas in insects 
they are bent or form an angle, often very obtuse at the 
principal articulations, which occasions them to extend 
far beyond the body, and when long to inclose a propor- 
tionally greater space. The wings are the organs of 
motion with which the upper side of the trunk is fur- 
nished ; and these, though they are the instruments of 
flight, are in no other respect analogous to those of 
birds, which replace the anterior legs of quadrupeds, but 
approach nearer, both in substance and situation, to the 
fins of some fishes, and perhaps in some respects even 
to the leaves of plants. M. Latreille is of opinion, That 
the four wings or their representatives replace the four 
thoracic legs of the decapod Crustacea*. Upon this 
opinion, which shows great depth of research and prac- 
tical acumen, I shall have occasion to express my senti- 
ments when I come to treat more at large on the anatomy 
* Hor. Entomolog, 413—. 
VOL. Ill. E 
