THE CRAWFISH. 69 



10. If the swimmerets on the first and second seg- 

 ments of your specimen are large, it is a male ; if 

 they are small it is a female. 



The Ceplialotliorax. 



1. Lift up the free edge of the carapace. This 

 part of the carapace is the gill cover, or branchioste- 

 gite. Inside are the gills. 



2. How many pairs of legs? 



3. Examine one of the hind pair of legs. Of how 

 many segments is it composed? Draw. 



4. Examine the third pair of legs. Draw. 



5. Examine the first pair of legs. Draw. 



6. Find the third, second, and first pairs of maxil- 

 lipeds. Draw one of each pair. Can you find a main 

 stalk and two branches? 



7. Find the second and first pairs of maxillae. 

 Draw one of each. 



8. Find the mandibles. Find the mandibular 

 palpus. How many segments has it? If you pull off 

 the mandibles, you will probably find the large mus- 

 cles which move them. 



9. Find the gills. Draw one. How many gills? 

 What appendages bear gills, and how many gills be- 

 long to each of these gill-bearing appendages? 



10. In the front of the gill chamber, find the gill 

 scoop, or scaphognathite. To what appendage is it 

 attached? What is its use? What separates the gills 

 from the gill scoop? 



11. Find the antennae. Can you discover a main 

 stalk and two branches? The two branches are very 

 unlike each other. Draw. 



12. Find the antennules, or little antennae. Can 

 you find the main stalk and two branches? The two 

 branches are very similar. 



13. Find the ears, or otocysts, on the upper side of 

 the basal joint of the antennules. 



