THE ARTHROPODS 381 



built on the same plan of structure, and that a study of a 

 few selected specimens will enable one to understand almost 

 any other insect which may be seen. For such type studies 

 the grasshopper and butterfly will introduce the chief prin- 

 ciples of insect structure and life. 



323. Study of a Grasshopper. (L) This animal consists of body 

 and appendages. Notice three regions of the body, head; thorax, 

 with three pairs of legs ; and a segmented or jointed abdomen. Is 

 the grasshopper bilaterally 

 symmetrical ? Notice that 

 the body and appendages 

 have a hard covering, the 

 exo-skeleton. 



Abdomen. The tip of 

 the abdomen varies in the 

 two sexes. In the female 



the abdomen bears two Fl0 '. 13L Grasshopper, a, antenna: w, 

 . , , . wings ; t, tympanum or ear-membrane ; 



pairs of pointed structures ^ ovipositor . S) S pi rac les or breathing 

 which are of use in deposit- p0 rea ; I, base of leg. (From Hatschek.) 

 ing the eggs, and together 



they are known as the ovipositor. The end of the abdomen in the male 

 is turned upward. Count the rings or segments in the abdomen. On 

 the first ring next to the thorax there is on either side a shining oval 

 patch, the organ of hearing. Along each side of the abdomen is 

 a groove, and just above it is a row of pores (spiracles or breathing 

 pores}. Watch the breathing movements of the abdomen of a living 

 specimen. The spiracles are connected inside with a system of 

 branched air-tubes (Irachece), which ramify through the body and 

 distribute air directly to the tissues. Compare this method of 

 respiration, which is characteristic of insects, with that of the frog. 



Thorax. Judging from the pairs of jointed appendages (legs), 

 how many segments in the thorax ? How many pairs of wings ? 

 Are they attached to first (anterior), second, or third segment? 



Look for the breathing-pores on the second and third segments. 



Examine the two wings and compare them as to form, size, 

 texture, color, position, and use. The veins in the wings are hollow 

 tubes which carry blood and air. 



The characteristic shrill sound made by katydids is caused by 

 rubbing the upper wing on the lower wing. 



Compare legs from each segment of the body which bears thorn. 



