8 PHYLUM ARTHROPODA 



beneath the forward wings. Each somite bears a pair of legs on its 

 ventral surface. The cuticula of each thoracic somite is composed 

 of a number of distinct plates. 



The abdomen is made up of eleven somites, which, however, 

 are not all perfect segments, the ventral portion of several of the 

 terminal somites being wanting. The posterior end of the abdo- 

 men is different in the two sexes, the female possessing an ovi- 

 positor, by means of which she buries her eggs in the ground. 

 The ventral portions of the ninth, tenth, and eleventh somites are 

 wanting in the female, the last complete somite being the eighth. 

 The dorsal portions of the three terminal somites, however, are 

 present. Projecting from the hinder end of the abdomen is the 

 ovipositor, which consists of two pairs of short, movable, curved, 

 and pointed structures. One of these pairs is dorsal in position, 

 and the anus is at its base ; the other is ventral, and at its base is 

 the external opening of the oviduct. Extending from the posterior 

 border of the tenth somite is another pair of pointed projections, 

 called cerci, which may have a sensory function. Just beneath 

 each cercus is a plate called a podical plate, which forms the hinder 

 end of the body. Between the two podical plates on the dorsal 

 side of the animal is the small, triangular eleventh somite. 



In the male an additional ventral plate, called the genital plate, 

 forms the hinder end of the body ; the podical plates and the cerci 

 are large. The eleventh somite is a small, triangular plate, dor- 

 sally situated, beneath which is the anus. 



On the lateral side of the first abdominal segment note the 

 auditory organ, a large, circular opening covered by a membrane. 

 With the aid of a hand lens find the spiracles of the thorax and 

 the abdomen. Ten pairs are present, one pair on the anterior 

 margin of both the mesothoracic and the metathoracic segments, 

 and one pair on each of the eight anterior abdominal segments, 

 that on the first abdominal segment being just within the margin 

 of the auditory organ. 



Exercise 1. Spread out and pin down all four wings and draw an 

 outline of the dorsal aspect of the grasshopper on a scale of 2 to 4. 

 Number the thoracic and the abdominal segments and label all 

 the parts observed. 



