CRAYFISH 



(Materials: Tags, carmine, pipettes, pins) 



Classification : — Phylum Arthropoda, Class Crustacea, Or- 

 der Decaj)oda, 



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. 



All crayfishes of the eastern United States belong to the 

 single genus Cambarus. There are many species of this genus 

 but all of them agree so closely in general structure that this 

 outline is suited for the study of any member of the group, 



I. The Live Aniwal 



1. Place a crayfish 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 crayfish in water and observe the movements 

 of the swhnmerets 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 crayfish in the air for a few minutes, then 

 return it to the water, back do^vnward, 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 



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