CHAPTER XVII 



PHYLUM XI. ARTHROPODA 



304. 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. 



305. The Fresh -water Crayfish (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 ap- 

 pendages. Describe the manner and purpose of these motions 

 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 ? 



5. Evidences of sensitiveness: Devise experiments of your 

 own to prove whether the crayfish is stimulated by light; 

 contacts; the presence of food in any other way than by sight; 



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