REPRESENTATIVE INSECTS 349 



pair. When these four pieces are brought together, their points 

 are in contact, forming a sharp organ by means of which the fe- 

 male bores the holes in the ground in which to deposit her eggs. 

 The third set of plates are known as the egg guides. These are 

 much smaller and are located median to the plates of the true 

 ovipositor. 



There are ten pairs of spiracles, or openings in the respiratory 

 system on the body of the grasshopper. Two pairs of these liplike 

 structures are situated on each side of the thorax on the anterior 

 margin of the pleural plates. The mesothoracic spiracle is con- 

 cealed by the posterior edge of the pronotum. The metathoracic 

 spiracle is located just dorsal to the mesothoracic leg, near the 

 suture separating the two segments. There is another spiracle just 

 dorsal to the attachment of the metathoracic leg, but this belongs 

 to the first abdominal segment. From the second to the eighth 

 abdominal segments there is one pair of spiracles located on the 

 anterior margin of each segment near the union of the sternum and 

 tergum. The spiracles are one of the most useful sets of structures 

 for determining the segmentation of an adult insect body. This is 

 because there are never more than eight pairs of abdominal spiracles 

 present in any fully developed insect. Air passes through the 

 spiracles into the tracheae and is carried to the tissues of the body. 

 This unique system of breathing enables the insect to keep the body 

 tissues well aerated and the carbon dioxide eliminated from the 

 body. 



The circulator}^ system consists of a single dorsal tube, or heart, 

 which extends along the length of the median dorsal part of the 

 body. In the abdomen of the fully developed insect this vessel is 

 divided into a number of chambers with side valves, which allows 

 the blood to enter but not to escape, except through the vessel 

 toward the head. Due to the pulsating of this portion of the tube, 

 which has been called the heart, the blood is forced to the anterior 

 part of the body where it flows out into the body cavity and slowly 

 returns to the abdominal region. In this process the tissues are 

 supplied with nourishment from the food materials carried in the 

 blood. It will be noted that the circulatory system has practically 

 nothing to do with the carrying of oxygen to the tissues. 



The digestive system of the grasshopper consists of a practically 

 straight tube extending from the mouth to the anus through the 



