348 



LECTURE XVI. 



Every Insect has a distinct head {Jig. 140, 141, a\ provided with one 

 pair of antennae (c), and every true or Hexapod Insect has its trunk 

 divided into two regions, called thorax {d^J /,) and abdomen {ah). 



140 



^"'^^ 141 



lulus. 



Locusta. 



The thorax is interposed between the head and the abdomen, and 

 so far is analogous to that part in human anatomy ; but it has 

 neither the same relation to the contained viscera nor to the locomo- 

 tive extremities which characterises the thorax in the vertebrate 

 animals. To the Insect's thorax are attached all the locomotive 

 members ; both the first pair, which may be compared with the pec- 

 toral extremities of the vertebrate animal, and the last pair, which 

 are analogous to the pelvic members, as well as the middle pair, to 

 which there is no correlative in the vertebrate series. This centre of 

 the locomotive powers is divided into three segments, which corre- 

 spond with the three pairs of legs : the first segment is termed the 

 " pro-thorax " {d\ the second the " meso-thorax " (/), and the third 

 the " meta-thorax " {%). Each of these segments has a dorsal and a 

 sternal piece : the dorsal half-rings are called respectively " prono- 

 tum," " mesonotum," and *' metanotum ; " the ventral or sternal arcs 

 bear the corresponding terms, " prosternum," '' mesosternum," and 

 " metasternum." From the inferior arches of the segments, the legs 

 (e, A, k) are developed, or with them they are principally articulated, 



