EXERCISE 93 



There are many organisms that respond to light without being able to see things as we see them, 

 and some of them do not even have eyes. 



Problem. How does an organism without eyes respond to light ? 



What to use. Live earthworms ; glass or enamel-ware dish ; some earth. 



What to do. Place earthworm in empty dish which has been moistened. Hold it so that the light 

 strikes it, and note the character and direction of its movements. Change position of dish to get illumi- 

 nation from different directions. Place earth in the dish and the worm on top of the earth ; note 

 whether the movements with relation to light are different on the earth. After the animal has started 

 to burrow, note the effect of stronger or weaker illumination on the exposed parts. 



Record. Describe the movements of the animals under different conditions and degrees of illumination. 



Questions. 1. What other organisms without eyes do you know to be sensitive to light ? 



2. Can you tell whether the front end or the rear end of the earthworm is more sensitive ? 



3. How can you tell that the movements observed were not responses to odor ? 



4. What other forces appear to influence the movements of the earthworm besides light ? 



[100] 



