202 ARTHROPODA 



sternum. Is the abdomen more movable than the other por- 

 tions? Of what advantage is this condition? The posterior 

 ends of the abdomens of male and female differ. This portion 

 of the female is modified to form the ovipositor, which con- 

 sists of two large pairs of plates that inclose a smaller pair 

 of plates. It is between these plates that the oviduct opens. 

 What advantage lies in the fact that 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 

 appendages 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 appen- 

 dages. With fine scissors remove it and place it in a watch 

 glass containing 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 maxillae. With a needle push one to one 

 side and notice that it consists of a somewhat flattened por- 

 tion 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? Re- 

 move them with scissors and place them in the watch glass 

 with the labrum, in approximately their relative positions 

 and study carefully. 



4. Pass a needle behind the remaining appendage, the 



