ADAPTATION AND AGGREGATION 237 



the process of feeding, but too much is fatal. Stentor 

 coeruleus, Amoeba and myxomycetes thrive in total dark- 

 ness. They are always found in regions of comparatively 

 low light intensity. The same is true of fly larvae. Nega- 

 tive response to light tends to keep these creatures buried in 

 cadavers where they find food. It is ordinarily only under 

 artificial conditions that the reactions of organisms to light 

 prove fatal. Positive reactions to candle, lamp and light- 

 house destroy untold numbers of moths and flies and bees 

 and beetles and birds, but who has seen such fatalities under 

 natural conditions ! Under such conditions the responses 

 to light direct these animals to the advantage of their well- 

 being. When an insect or a bird in a room, a bee in a flower 

 or a pomace fly in a wormhole of a decaying apple is excited 

 it flies directly toward the light and ordinarily escapes. It 

 could not be expected to react differently in the presence of 

 a candle surrounded by darkness, since it receives the same 

 general stimulation and has had no experience with the 

 consequences. Many water-inhabiting larvae are strongly 

 positive even in light so intense that it is injurious. They 

 do not become negative and escape danger. Under natural 

 conditions the strong positive response serves to scatter 

 them far and wide, and under such conditions there is no 

 need for a negative response. The surface of the water 

 limits the distance they can proceed toward the light and in 

 their natural environment they experience none of sufficient 

 intensity to be injurious. As they grow older many of them 

 lose their positiveness and become negative, and now their 

 reactions guide them to the bottom into dark places, where 

 they spend most of their adult life. 



Sand fleas are usually found in dark places under masses 

 of seaweed on the beach. If they are disturbed they 

 become strongly positive. This response directs them 

 toward the water, from which the stronger light usually 

 comes. After they are in the water they become negative. 

 This response directs them to the bottom and into dark 

 crevices. Under natural conditions their reactions to light 



