166 [ARTHROPODA. 



wings are folded so they may be covered by the anterior. Does 

 this seem to greatly reduce their strength? 1 



3. The Abdomen. Count the number of segments. Each 

 one is covered dorsally by a tergum and ventrally by a sternum. 

 Why should the abdomen be more movable than the other por- 

 tions? The posterior ends of the abdomens of male and female 

 differ. This portion of the female is modified to form the ovi- 

 positor, which consists of two large pairs of plates that inclose 

 a smaller pair of plates. It is between these plates that the 

 oviduct opens. Why do the larger plates possess hard tips? 

 Along the sides of the abdomen notice the stigmata, the external 

 openings of the respiratory system. Do you find stigmata on 

 other parts of the body? 



Draw an enlarged side view of a grasshopper, placing the appen- 

 dages in their proper positions. 



Mouth Parts. It has already been noticed that the mouth 

 parts serve to cut off pieces of leaves, which are then passed 

 directly into the alimentary canal. For such a purpose there 

 should be holding as well as cutting parts. 



1. Pass a needle under the labrum, which forms the upper 

 lip, and notice that it is hinged and that the end is lobed. It is 

 not supposed to be homologous with usual arthropod appendages. 

 With fine scissors remove it and place it in a watch-glass contain- 

 ing water. 



2. Immediately behind the labrum is a pair of hard, dark- 

 colored organs, the mandibles, that are used in cutting the food. 

 Their position should be carefully noted, but it will be better 

 to leave them in position until the other mouth appendages 

 have been removed. 



3. Situated by the side of the mouth and just behind the 

 mandibles are the maxillce. With a needle push one to one side 

 and notice that it consists of a somewhat flattened portion with 

 a jointed maxillary palp at one side. Carefully determine the 

 positions of the maxillae with relation to other parts. What 

 possible uses are served by the two parts? Remove them with 



1 You should examine the posterior wing of a beetle and see how it 

 is folded. 



