280 ELEMENTARY ENTOMOLOGY 



these segments are made up of separate plates, held together by 

 a tough, connecting membrane. These plates may, however, be 

 divided into three groups : the tergum, or dorsal region ; the 

 sternum, or ventral region ; and the pleuron, or lateral region. On 

 the dorsal and ventral regions of the body the sutures separating the 

 mesothorax from the metathorax are not very distinct. On the sides 

 of the body, however, there is a very distinct line, or suture, running 

 from the posterior border of the attachment of the second pair 

 of legs toward the dorsal part of the body. This suture divides 

 the mesothorax from the metathorax. The pleura of each of the 

 posterior thoracic segments are again divided by transverse sutures, 

 so that each pleuron consists of two sclerites. 



a. The legs. The mesothoracic and metathoracic legs arise from 

 the lower posterior border of the pleura of their respective seg- 

 ments, and are joined to the thorax by a tough, elastic membrane. 



b. The wings. The wings have a more anterior origin in respect 

 to their thoracic segments than do the legs. Each pair arises at 

 the union of the pleura and tergum. 



c. The spiracles. The spiracles, or openings of the respiratory 

 system, consist of two pair of liplike structures situated on either 

 side of the body on the anterior margin of the pleural plates. The 

 mesothoracic spiracle is concealed by the posterior edge of the 

 pronotum. The metathoracic spiracle is located just dorsal to 

 the mesothoracic leg, near the suture separating the two segments. 

 There is another spiracle just dorsal to the attachment of the meta- 

 thoracic leg, but this belongs to the first abdominal segment. 



Exercise 6. Make a full-page drawing of a side view of the thorax of a 

 locust with the wings and legs removed, showing all of the parts noted above. 



SECTION IV. THE THORACIC APPENDAGES 



Material. With a pair of fine-pointed scissors remove the legs from one 

 side of the body of the locust and arrange them on a piece of white paper in 

 their regular order. Also remove the wing and wing-cover (mesothoracic wing) 

 from one side and pin to a thin sheet of cork, spreading the wing to its full 

 dimension. 



1. Legs. Make a comparative study of the legs, which will be 

 found to consist of the following segments : 



