108 NATURE STUDY REVIEW [8 :3— Mar., 1912 



ing of its "'tail," the easiest way to catch one is to put a net back 

 of it and then annoy it by the hand or boot, when it springs into 

 the net itself. 



4. Observations may be made on the methods of locomo- 

 tion — whether backward or forward, swimming or walking — and 

 what appendages are used in each. 



5. How does the crayfish defend itself? Factors suggested 

 might be nocturnal habits, hard covering, habit of hiding under 

 stones, habit of springing up when disturbed, great claws, and so 

 forth. 



G. Whether or not crayfish are sensitive to light is easily dem- 

 onstrated. Cover one side of the vessel containing crayfish and 

 see how quickly they will collect in the shaded area, if not dis- 

 turbed. A discussion of their natural environment will bring out 

 reasons why this is of advantage to the animal. 



7. There is most interesting material for observation in the 

 actual process of eating. Does the crayfish distinguish food by 

 sight or touch ? How does it grasp it ? How tear it up ? Has it 

 jaws? These and other questions will readily suggest themselves 

 to the pupil and can be answered by first hand knowledge. 



8. To determine just how the crayfish breathes is another 

 little problem. First, lift a crayfish from the water for a few 

 moments. On returning it to the water air bubbles will come from 

 near the mouth. After observing this, the experiment of put- 

 ting a little carmine solution or ink near the anterior end of the 

 abdomen of a crayfish held on its back, will show where the 

 water enters and where it leaves the gill chamber. By pulling 

 ofif the mouth parts of a dead crayfish, the "gill-bailer," a thin, 

 transparent structure on one of the mouth parts, is easily found. 

 Its function is to keep a current of water going through the gills. 

 By cutting away the carapace, or hard outer covering of the dead 

 animal, the gills will be seen and the gill-bailer made out. I 

 have found that a comparison of the crayfish gills and human 

 lungs makes an interesting and efficient illustration for a physi- 

 ology lesson on the structure and function of the latter. 



9. The fact that a crayfish carries its skeleton outside instead 

 of inside, is usually a new idea. When the pupil observes the 

 process of moulting and sees the whole external skeleton shed so 

 that the animal can grow, he has taken one step further toward 

 an appreciation of the wonderful adaptations in nature. The 

 questions naturally arise as to what parts are in the cast-off shell 

 and why the crayfish is soft-shelled at this time. 



10. How does a crayfish move its appendages when it walks? 



