THE LOCUST 161 



Examine them carefully with a lens. Press the digestive tract to one 

 side and find some of the larger tracheal tubes as they pass from the 

 internal organs to the spiracles in the body wall. At places you may 

 also see air-sacs, which arc enlarged portions of the tracheal system. 

 Take a bit of muscle from one of the legs of the insect, mount on a 

 slide in water, tease apart, and study with the compound microscope. 

 Notice the muscle fibers and the fine, branching tracheae. Minute 

 branches of the air-tubes extend to all parts of the body, running not 

 only among the cells but actually passing into and through the cells, 

 thus bringing the inspired air in intimate contact with the protoplasm. 

 Compare the manner of distributing oxygen in the frog and locust. 

 IVIake a drawing of part of such a preparation. 



Exercise 7. — The Excretory System. 



(e) Notice the numerous small, brown, crooked tubules on the 

 surface of the digestive tract in the abdominal region; use the lens to 

 distinguish them from the silvery-white tracheae with which they are 

 interlaced. These are the Malpighian tubes, which are the excretory 

 organs of the insect. Where do they connect with the digestive tract? 



Exercise 8. — The Digestive System. 



(f) The digestive tract has the following parts: the esophagus, 

 which lies in the head and cannot be seen fully until later; the crop, 

 an enlarged portion in the thorax; the gastric caeca, several pairs of 

 digestive glands which surround the tract and empty into it between 

 the crop and the stomach; the stomach, which extends from the crop 

 to the region where the Malpighian tubes are attached; the intestine, 

 which extends to the anus. The intestine has a more slender part, 

 called the colon, near its middle and terminates in a larger part, the 

 rectum. Make a drawing of the digestive tract as seen from the side 

 ( X 4) , surrounded by a simple outline of the entire animal. 



Exercise 9. — The Nervous System. 



(g) Remove the digestive tract by cutting it across at the esophagus 

 and the rectum. The nervous system, which lies along the mid- 

 ventral line, can now be seen in the abdominal region. It should be 

 carefully exposed by picking away other tissues, and working forward 

 until you have exposed the parts in the thoracic region and head. As 

 in the crayfish, the nervous system consists of masses called ganglia, 

 connected with each other by ventral, longitudinal nerve trunks. Each 

 ganglion gives ofT nerves to surrounding parts of the body. The appar- 

 ently single ganglionic masses are each composed of fused right and left 



