A GRASSHOPPER. 71 



have made the next drawing split open the crop, rinse it and 

 examine the grinding structures in the lining. The ventriculus 

 extends posteriorly to just in front of the line of attachment of a 

 great many tangled brown threads, the Malpighian tubules, 

 having an excretory function similar to that of the kidneys in 

 higher animals. The intestine ends in the anus at the base of the 

 dorsal pair of ovipositors. How does the length of the digestive 

 tract compare with the length of the body ? 



Exercise 10. Draw the alimentary tract in its natural position, using 

 the outline of the entire body. 



Technical Note. Snip off the alimentary canal at the base of the head 

 and near the amis, remove, and rinse the specimen with clean water. 

 Cut away the hard covering from the top of the head. 



e) Between the eyes observe a light-colored mass, the brain or supra- 



cesophageal ganglion. Trace out its connection, by means of 

 commissures, with the suboesophageal ganglion lying beneath 

 the oesophagus. From this ganglion a nerve cord extends to the 

 posterior end of the abdomen along the ventral body wall. Follow 

 it out and determine the number of thoracic and abdominal 

 ganglia. Look for fine nerves branching off from the ganglia. 

 Does the ventral nerve cord appear to be double ? 



Exercise n. Make a diagram of the nervous tract. 



f) The circulatory system is relatively simple in an insect. A delicate 



pulsating tube called the heart extends along the dorsal side of the 

 abdomen. It was probably torn in dissecting the specimen, but 

 even under the most favoring circumstances it is quite hard to 

 make out. In its walls are some valvular openings through which 

 a body fluid corresponding to blood is drawn in and pumped for- 

 ward, returning again through the body spaces or cavities. Ex- 

 plain the interdependence of a simple blood circulatory system 

 and a complex tracheal respiratory system. 



