DEFINITION OF THE TERM INSECT. 49 



invariably six in all insects, with the exception of the 

 Octopods or most of the Trachean Arac/mida, which have 

 usually eight. 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 situation of their legs; 

 for though the anterior pair or arms are analogous in 

 that respect, the posterior pair are not, since in quadru- 

 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 pairs 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, lut 

 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. LatreilJe 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 



8 Hor. Entomolog. 413 — . 

 VOL. Til. E 



