STUDY VI. ARTHROPODA. Joint-footed 

 Animals. 



Central idea : Differentiation and homology. 



1. THE CRAYFISH. 



A. Habitat. 



1. Where would you look for crayfish ? 



2. How can you catch them ? 



3. Where do they make burrows ? Why ? 



4. How can you recognize the burrows ? 



B. General Observations. 



1. Compare the shape of the dorsal and ventral sur- 



faces. 



2. What is the color of the living crayfish ? 



3. How is this color of any use to the crayfish ? 



4. Identify two distinct regions of the body, — an ante- 



rior region (cephalo-thorax) and a flexible posterior 

 region (abdomen). 



5. In what ways are the differences between the ante- 



rior and posterior ends more marked than in the 

 earthworm ? 



C. The Shell. (Exoskeleton.) 



1. Does the shell cover every part of the animal ? 



2. How is the shell modified at the joints to permit 



movement ? 



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