ARTHROPODA. 57 



6. Mouth parts. 



a. Labrum, the upper lip. What is its shape ? Is it 



movable ? 

 J. labium, the lower lip. Compare it with the 



labrum. Observe the three-jointed palps. 

 c. Mandibles, strong, dark jaws situated under the 

 labrum. Observe their relation to the mouth 

 and notice the cutting teeth on them. 

 d Maxillae. 



These are situated just in front of the labium 

 and are each composed of three parts ; a cutting 

 tooth, a spoon and a five-jointed palp. 

 What is the function of each of the mouth parts ? 

 What are the palps for ? 



In what direction with relation to the body must 

 the grasshopper hold its food in order to chew 

 or to bite it ? 

 Can you think of any reason for the notches in 

 the lips ? 



D. The Thorax and Its Appendages. 



1. Observe the division of the thorax into three seg- 



ments, each of which has a pair of legs. The 

 segments are named in order from the anterior 

 end prothorax, mesotborax and metathorax. 



2. The Legs. 



a. Observe that the first and second pairs of legs have 

 a lateral direction with relation to the body, 

 while the third pair extend posteriorly. 



h. Observe also the difference in size between the 

 third, and the first and second pairs of legs. 



c. Why is the third pair of legs different from the 

 other two pairs ? 



