Insecta. 13 



abdomen. The under part of the abdomen, included between 

 these grooves, is the sternum, the side of the abdomen is called the 

 pleurum, and the upper part is the tergum. 



3. Just above the groove that separates the sternum from the 

 pleurum is a row of small holes, the breathing pores, or spiracles ; 

 count them. 



4. In a live specimen, watch the movements of breathing. 

 All insects breathe by means of a complicated system of air 

 tubes, the tracheae, which branch from the spiracles throughout the 

 body. Can the grasshopper be drowned by holding its head 

 under water? Connected with the air tubes, in grasshoppers and 

 other strong flying insects, as bees and flies, are large air sacs, 

 which fill with air, and are said to aid, like balloons, in keep- 

 ing the insect in the air. By carefully cutting away the roof of 

 the abdomen, these air sacs may be seen, marked by their white 

 walls ; the white air tubes, or tracheae, may also be readily seen. 



5. Under the bases of the wings, on the first abdominal ring, is 

 a pair of thin, shiny, oval membranes, the tympana, or ear- 

 drums. The inner surface of each tympanum is connected with 

 a nerve. 



6. The abdomen of the female ends in four points ; in laying 

 the eggs these points are first pressed together, then thrust into 

 the ground, and then separated ; this process is repeated till a 

 hole is made, sometimes as deep as the abdomen is long, at the 

 bottom of which the eggs are deposited, passing out between the 

 four points, which together are called the ovipositor. The males 

 are smaller than the females. Draw the abdomen, as seen from 

 the sides, of both the male and the female. Take now an entire 

 specimen and draw a side view of it. 



INTERNAL STRUCTURE OF THE GRASSHOPPER. 



This work would better be done after the student has dissected 

 the crayfish. Dissect under water in the dissecting pan. 



i. Get a large female grasshopper, freshly killed. Cut off the 

 wings, and place the specimen, back uppermost, in the dissecting 



