AETHBOPODA. 51 



in the thorax? How many in the ab- 

 domen ? 



M. Suggestive Questions. 



1. What kind of localities do crayfish prefer ? 



2. Why are there no crayfish in " granite New Eng- 



land"? 



3. Why cannot crayfish readily catch live animals for 



food? 



4. Why does the crayfish sometimes leave the streams? 



5. Is the crayfish edible ? 



6. How are they caught by fishermen ? 



7. When is the breeding season ? 



8. How do they care for their eggs and young ? 



9. Turn a crayfish over on its back. Is there coor- 



dination in its movements to right itself ? 



10. Compare the position of the mouth in the earth- 



worm, the marine worm and the crayfish. What 

 relation does this change of position have to the 

 development of a head ? 



11. Compare the earthworm and the crayfish in respect 



to the following characteristics, placing the 



answers in parallel columns, — 

 (a) segmentation ; 

 (6) exoskeleton ; 

 (c) appendages ; 

 (d?) regions of the body. 



2. THE CRAB. 



A. The Regions of the Body. 



1. Identify cephalo-thorax and abdomen. 



2. How does the width of the cephalo-thorax compare 



with its antero-posterior dimension? 



