94 A GUIDE FOR THE STUDY OF ANIMALS 



when contracted? Of what substance is the coral com- 

 posed ? 



4. Describe the exoskeleton of a starfish. Contrast the 

 exoskeleton of the sea urchin and the starfish. Why does 

 a sea cucumber need no well-developed exoskeleton .'' 



5. What structure in an earthworm may be considered 

 an exoskeleton.' What other types of exoskeletons are 

 found in segmented worms ? 



6. Of what substance is the exoskeleton of arthropods 

 composed .■• What additional substance is found deposited 

 in the shell in the case of crustaceans ? What advantage 

 in the arthropod type of exoskeleton ? 



7. Why are mollusks so commonly called " shellfish " ? 

 What advantage in the mollusk type of skeleton ? What 

 disadvantages ? 



Summary. 



1. What type of exoskeleton is common among inverte- 

 brates } 



2. What are the general purposes of exoskeletons ? 



3. What is the explanation of the various forms of exo- 

 skeletons' found .'• 



4. Of what substances are exoskeletons composed } 



B. Protective Coloration 



71? show how Color may be Protective 

 Materials. 



Specimens such as the Kny-Scheerer mimicry collections, 

 diagrams, etc. 



Definitions. 



General protective resemblance, the general resemblance 

 between the color of an animal and its surroundings. 



