INSECTS, AND THEIR RELATION TO MAN 181 



e. Commensalism or Symbiosis 



Observations. 1. Study the case of the sea anemone with 

 many stinging cells, on the shell of a hermit crab. Just where 

 is the sea anemone located ? 



2. Note that sponges may also be found on the backs of some 

 crabs. 



Conclusions. 1. What advantage is the presence of the sea 

 anemone to the crab ? 



2. What are the advantages to the sea anemone because of 

 being on the back of the crab? Note. Where animals of 

 different sorts associate themselves for mutual benefit, it is 

 said to be a case of commensalism or symbiosis. 



f. Parasitism 



Observation. Many insects are parasitic as we have 

 seen some worms to be. How do the sucking lice get their 

 living ? 



Conclusions. 1. Are there any advantages to an animal that 

 adopts a parasitic life ? What disadvantages ? 



2. Give other examples of parasites among insects. 



Questions 



1. W T hat is " protective resemblance " ? Give three examples 

 you have studied. 



2. What is the meaning of the term "metamorphosis"? 



3. Give an account of grasshopper migrations and plagues. 



4. Could you drown a grasshopper by holding its head 

 under water ? 



5. What is meant by the ' economic importance 7 of an 

 insect ? 



6. What sort of metamorphosis has a locust ? 



7. When is the best time to collect cocoons ? 



8. How may insects " shift for a living " ? 



9. What is the meaning of the following : 



