104 LAHOUATORY STUDIES IK ZOOLOCY 



All Www p;iirs of legs of the grasshopper are used iu walking, 

 but the third pair are primarily jumping legs and show structural 

 modifications for such a use. Remove a walking leg from the 

 right side of the body and study. It has five parts. The short 

 joint next to the body is the coxa. The second segment or 

 trochanter is smaller than the coxa, its ventral aspect being longer 

 than the dorsal. This segment is succeeded by the long femur. 

 Distad of this is placed the slender, spiny tibia, while the tarsus 

 includes all that part of the leg distad of the tibia. It consists 

 of three segments. The last segment of the tarsus bears a pair 

 of claws and a single cushion or pulvillus. In addition there are 

 four pairs of pulvilli under the other segments of the tarsus. 

 Compare the jumping leg with the other walking legs as to 

 relative proportions of parts and direction of the convexities 

 of the articulations. 



In the membrane along the sides of the thorax, just cephalad 

 of the mesothorax, is a small opening. This is the mesothoracic 

 spiracle, one of the openings of the respiratory system. Notice 

 also on the pleural suture which separates the mesothorax from 

 the metathorax a similar opening, the metathoracic spiracle. 

 Both openings are guarded by lips. 



The Abdomen and Its Appendages. — Each complete segment 

 of the abdomen consists of an inverted U-shaped tergum bearing 

 on its ventral border a slight indentation, the abdominal spiracle. 

 This arched plate is probably a fused tergum and pleuron. There 

 is a convex ventral plate, the sternum. The rest of the pleuron 

 is represented by the membranous fold where tergum and 

 sternum articulate. 



The sternum and tergum of the first abdominal segment are 

 separated from each other by the depression for the insertion of 

 the third pair of legs. The tergum of this segment bears upon 

 either side a kidney-shaped opening, covered by a thin, semi- 

 transparent membrane. This is the chordotonal organ, erroneously 

 called an ear. On the anterior border of the chordotonal organ 

 is the first abdominal spiracle. How many spiracles are present 

 on the body of the grasshopper? 



The next seven segments are alike in both sexes but the remain- 

 der of the abdomen is different in form and structure in the 

 male and female. In both sexes the ninth and tenth terga are 

 narrow and partially fused on their lateral margins. The 

 eleventh tergum or suranal plate extends caudad forming the roof 



