160 THE LOCUST 



II. INTERNAL STRUCTURE 



Exercise 4. — -General Internal Structure. 



(a) Cut off the legs. With scissors, cut through the exoskeleton 

 along each side of the thorax and abdomen just above the spiracles, 

 being careful not to cut deep enough to injure internal structures. 

 Carefully remove the dorsal part of the exoskeleton, and before dis- 

 carding it, look for the heart, which usually comes off attached along 

 the mid-line. If the tliin mass of muscles, which clings to the piece in 

 the abdominal region, is carefully stripped away by grasping with 

 forceps at the posterior end and pulling forward, the heart will per- 

 haps be seen as a delicate tube lying upon the dorsal surface of the 

 muscles. How far can you trace the heart anteriorly? Can you see 

 the openings, or ostia, along its sides by using the handlens? Cut off 

 the top of the head nearly as far down as the bases of the antennse, 

 being careful not to break the head from the body. Pin the animal 

 down under water by two pins through the bases of the jumping legs 

 and keep it under water for the following dissections of the internal 

 organs. 



(b) The digestive tract is now exposed in the thorax and anterior 

 part of the abdomen. In the posterior part of the body, portions of 

 the reproductive organs occupy a dorsal and lateral position and hide 

 the digestive tract. These organs are somewhat obscured by the lace- 

 like fat-body, which should be carefully picked away from the top of 

 the digestive and reproductive organs. 



Exercise 5. — The Reproductive System. 



(c) If the specimen is a female, the ovaries will be seen as a large 

 mass containing many good-sized, elongated eggs. If it is a male, the 

 testes will form a compact mass in the posterior part of the abdomen. 

 In both sexes, the ducts from right and left reproductive organs unite 

 ventral to the digestive tract and discharge through an opening at the 

 tip of the abdomen. These features are not easy to study, and the 

 reproductive organs may now be removed to expose fully the digestive 

 tract. 



Exercise 6. — The Respiratory System. 



(d) The respiratory organs of insects are air-tubes called tracheae, 

 opening to the outside by means of the spiracles, which have been pre- 

 viously observed on the outer surface of the body. The trachea; may 

 be seen as silvery-white tubes on the surface of the digestive tract, if 

 they contain air, but if they contain fluid they will be hard to see. 



