Orientation 215 



but these animals do not generally swim upwards to the surface of 

 the water toward the sun since the diffuse side illumination in the 

 ocean inhibits the reaction to a single source (Schallek, 1943). 



The familiar "bee-line" course which the honeybee takes from its 

 hive to a source of food is determined as a definite angle to the direc- 

 tion of the sun. The bee does not fly directly toward or away from 

 the sun, but orients at an angle to the changing azimuth of the sun. 

 Upon returning to the hive, the bee communicates to its fellow work- 

 ers by a special "wagging dance" both the approximate distance and 

 the direction relative to the sun of the food that it has discovered. 

 Still more remarkable is the fact that the worker bee is not required 

 to see the sun directly but can be oriented by a small patch of blue 

 sky. The bee's compound eye has been shown to be sensitive to the 

 angle of polarization of sky light, and the bee apparently uses this 

 information in combination with other orienting forces to determine 

 the proper line of flight when the sun is obscured. The bee usually 

 restricts its visits to one species of plant at a time— a fact that is of 

 obvious advantage both to the bee's efficiency and to the plant's 

 successful pollination. Flower species are recognized by shape, scent, 

 and color; the bee's eye can distinguish yellow, blue-green, blue, and 

 ultraviolet, but it is blind to red (von Frisch, 1950). 



The ability of homing and migrating birds and fish to find their 

 way over long distances is perhaps even more amazing. The precise 

 method of navigation used by such far-ranging vertebrates has mysti- 

 fied observers for generations. Although birds may use landmarks, 

 persisting cloud formations, prevailing winds, and other ecological 

 cues to some extent, these possibilities do not appear to explain all 

 instances (Griffin, 1952). Evidence has been obtained that certain 

 species of birds may use the direction of sunlight as a means of 

 orientation and that the birds are able to allow for the change in the 

 sun's position during the day (Kramer, 1952). 



Under natural conditions the direction of growth or of locomotion 

 of plants or of animals is usually determined by several different in- 

 fluences acting simultaneously. In addition to such common orient- 

 ing factors as light, gravity, temperature, and moisture, certain species 

 may be guided by sound or other types of vibration, by scent or other 

 chemical sense, or by other special reactions to environmental 

 stimuli. We know that tropistic and tactic responses play a very large 

 role in the lives of most lower organisms in nature. Reactions to the 

 direction and intensity of the orienting influences of the habitat are 

 responsible for getting motile organisms where we find them. In 

 order to understand the mechanism of distribution of these forms, 



