LOBSTEE OE CEAYFISH IVl 



showing the various functions which a typical append- 

 age, though modified in different ways, may perform. 

 Do you find here a close relationship between structure 

 and function ? Can you determine whether the struct- 

 ure of. an organ determines the function which it can 

 perform, or vice versa ? 



What means of protection from its enemies has the 

 animal? What means of defence ? Of offence? When 

 the animal is moving along, does it co-ordinate the move- 

 ments of its various appendages — i. e., do all of the ap- 

 pendages work together for the accomplishment of a 

 certain object ? Turn a live specimen over on its back. 

 In righting itself, does the animal show co-ordinated 

 motions of the appendages ? 



Compare the lobster or the crayfish with the earth- 

 worm as regards the plan upon which the body is con- 

 structed, the collection of the segments or metameres 

 into well-defined regions, the arrangement and structure 

 of the appendages, the number, position, and structure 

 of the sense organs, the structure of the muscular, the 

 nervous, and the digestive systems, etc. Which is the 

 more complicated or " higher " animal ? Why ? 



Use the crab {Cancer or Gallinectes) for comparison. 



