THE MOTH AND THE CANDLE 235 



another, but to scare would-be predatory foes, such as 

 birds, bats, and reptiles. I have heard a story (which 

 I should like to have confirmed) that in some part of 

 tropical Asia a certain kind of bird collects half a dozen 

 or so of a species of glow-worm and places them at the 

 entrance to its nest, so as to scare nocturnal animals 

 which might attack its eggs or its young. It is a note- 

 worthy fact that a point of light in the dark may act in 

 two opposite ways on animals which see it — either it 

 attracts or it repels them. The physiologist calls this 

 positive and negative " photo-taxis " (light-guidance). 

 And we have the similarly positive and negative in- 

 fluence of chemical taste and smell, called " chemo-taxis," 

 and a similarly contrasted positive and negative " hygro- 

 taxis," or directive influence of moisture upon the move- 

 ments of animals and plants. 



I 



