CRAWFISH 



(Materials: Tags, carmine, pins) 



Classification : Phylum Arthropoda, Class Crustacea, Or- 

 der Decapoda. 



This animal is studied as an example of a complex seg- 

 mented animal, with diverse kinds of jointed appendages which 

 are built upon the same general plan, and thus clearly illustrates 

 the principle of homologies. 



I. THE LIVE ANIMAL 



1. Place a crawfish in a large dissecting pan and allow it 

 to walk about. Determine the function of the different legs. 

 Notes required on all questions upon live animal. 



2. Place the crawfish in water and observe the movements 

 of the swimmer 'ets on the ventral side of the abdomen. 



3. Note the use of the tail fin when the animal is suddenly 

 surprised in the water. 



4. Turn the animal upon its back and describe the method 

 of righting itself. This experiment should be tried upon a rough 

 surface. 



5. Keep the crawfish in the air for a few minutes, then 

 return it to the water, back downward, and describe where you 

 find bubbles of air escaping. 



6. Hold the animal, back downward, over a piece of white 

 paper in the water and place a drop of carmine suspension on the 

 ventral surface of the thorax in the region of the posterior pair 

 of legs. Describe the result. What is the relation between what 

 you observe and the bubbles, previously seen? The carmine is 

 used simply to show presence of and direction of water currents. 



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