194 The Animal Mind 



orientation ; the animal moves, for instance, always away 

 from the light, which means that it moves forward if its 

 body happens to be oriented with the tail to the light, or 

 backward if its head happens to be directed to the light. 

 Such behavior is reported by Holmes of mosqmto larvas 

 (338) and by Gee of leeches (257). On the other hand, 

 Hadley (274) says that young lobsters always orient with the 

 head towards the light, though they may move either away 

 from or towards it. In some animals with eyes, such as the 

 crustacean Daphnia, there is reason to think that body 

 orientation is primarily an affair of eye-orientation or fixa- 

 tion. This at least is the view of Radl (621). He placed 

 Daphnia under a microscope in such a way that only the 

 eyes could be moved. When the light coming from below 

 was diminished, the eyes rolled upward ; when the light 

 coming from above was diminished, the eyes rolled down- 

 ward. Holmes (330) observed that in amphipods, blacken- 

 ing one eye of a positively phototropic animal causes a 

 turning toward the blackened side, as if the animal were 

 trying to restore the missing illumination ; similar experi- 

 ments upon negative animals produced turning towards the 

 other side. 



It is the view of Loeb (434). that oriented response of 

 animals to light is wholly analogous to the same type of 

 response in plants. Since plants with their very slow and 

 limited movements are subject more to light as a continuous ^ 

 stimulus than to sudden changes in Hght intensity, orien- 

 tation in their case must be brought about by the steady and 

 continuous action of the light. Accordingly, Loeb main- 

 tains the view that the tropism or oriented response of 

 animals to light is dependent on the continuous action of 

 the Hght, and not on changes in light intensity. It is thus 

 a mode of response that has nothing in common with "sen- 



