66 LABORATORY DIRECTIONS IN 



shallow dishes containing water and a moderate amount of algae or a few 

 small pieces of water weed (Elodea). Allow these dishes to stand for some 

 time absolutely undisturbed and add no food. Where are the animals? 

 Why? What is the stimulus involved? As gently as possible, place 

 a small, recently excised portion of the body of an earthworm just below 

 the surface of the water. Watch the dish intently for signs of activity on 

 the part of the planarians. What kind of activity is manifested? What 

 is the end result of this activity? To what kind of stimulus is it a 

 response? Is it positive (going toward the source of the stimulus) or 

 negative (going in the reverse direction)? Of the stimuli referred to 

 above, which is the stronger? Evidences? 



2. Observe land sow-bugs (Porcellio sp.) in a petrie dish half of which 

 is covered with black paper to exclude the light, leaving the other half 

 well lighted. Ten sow-bugs have been placed in this dish and left undis- 

 turbed so that they might come to rest. What is the distribution of the 

 animals and how do you account for it? What is the stimulus involved 

 and how do they react to it? 



3. Observe ten land sow-bugs in another petrie dish half of which 

 contains loosely laid thin sheets of mica, the other half being clear. 

 In which half are most of the sow-bugs? Which of the following 

 factors, if any, are they reacting to: light, gravity, contact, moisture, 

 temperature? Reactions to these are called respectively, phototaxis, 

 geotaxis, thigmotaxis, hydrotaxis, and thermotaxis. 



4. In a pan half of the bottom of which is covered with rather moist 

 soil and half with dry soil note the reactions to moisture in this species of 

 land sow-bugs. 



Make records of observations. In what sort of environment would 

 you expect to find land sow-bugs? Do you conceive the reactions of 

 these animals to be advantageous to them? 



C. SUMMARY 



How are the animals studied in this exercise adapted to their envi- 

 ronment? Is the adaptation morphological, physiological, or both? 

 Examples. Have you witnessed any adaptation to the biological en- 

 vironment (the other organisms in the vicinity)? How may animals 

 have become adapted to their environment? (Give alternative views 

 if you can.) What is ecology? 



These questions are suggestive only, and are not intended to in dim ti- 

 the order in which topics are to be discussed in the summary, nor to limit 

 the summary to these topics. 



