CHAPTER XVII. 



PHYLUM VII. ARTHROPODA. 



297. This group is one especially favorable for the pupils 

 to study in the field, in the haunts of the animals themselves. 

 For this reason, wherever it is at all possible, the members of 

 the class should be required to collect a portion of the material 

 needed in the laboratory and to submit a report on such items 

 of physiology and ecology as may be expedient in each case. 

 The teacher will find suggestions in the supplementary 

 exercises. 



298. The Fresh-water Cray-fish (Cambarus). This form 

 should be studied when living specimens may be had. They 

 may be kept for considerable time in a tub containing an inch 

 of water. This should be changed every day or two. Feed 

 on small pieces of meat or earthworms. 



I. Physiology. 



1. Locomotion: walking; how effected? Swimming; how 

 'effected? Under what circumstances does the animal swim? 

 Do all the walking legs act together in walking? How many 

 are at rest at once? In what order do they act? 



2. Movements of the parts of the body: segments, and 

 appendages. Describe the manner and purpose of these mo- 

 tions as far as you can determine. In what different ways do 

 the various groups of appendages seem to act? Watch them, 

 one pair at a time. 



3. Feeding: kind of food used and manner of securing it. 



4. Respiration: by means of air or water? How can you 

 be sure? Does the animal do anything to renew the water, 

 by producing currents? Place a minute amount of carmine 

 or indigo solution at the side of the animal at the union of 

 the abdomen and thorax; at the front of the thorax. What is 

 the difference? What does it signify? 



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