52 STUDIES OF ANIMAL LIFE. 



3. How does the size of the cephalo-thorax compare 



with that of the abdomen ? 



4. What is the natural position of the abdomen with 



reference to the cephalo-thorax ? 



5. How does the number of somites in the abdomen of 



the crab compare with the number in the abdomen 

 of the crayfish ? 



6. Is the crab compressed or flattened ? 



7. Sketches. 



a. Make an outline sketch of the dorsal surface of 



the crab, omitting the appendages. 

 h. Make a similar sketch of the ventral surface. 



B. Cephalic Appendages. 



1. Identify the antennae, the eyes and the "mouth 

 parts." Indicate their position in the sketch for 

 A 7 J. 



C. Thoracic Appendages. 



1. Identify the pinchers and the walking-legs. Indi- 



cate their position in the sketch for A 7 6. 



2. How does the fifth pair of thoracic appendages differ 



in different species of crabs ? Why ? 



D. Abdominal Appendages. 



1. Identify the swimmerets. 



2. Are all the somites of the abdomen provided with 



appendages ? 

 What reasons can 3'ou suggest for the absence of a 

 caudal fin ? 



E. Suggestive Questions. 



1 . What is the habitat of the crabs you have studied ? 



