ATTRACTION OF LIGHT 21 



as that to artificial light (i.e., phototaxis in 

 the narrower sense). Professor Max Verworn, 

 whose work on General Physiology has done 

 so much to give precision to the interpretation 

 of elementary vital phenomena, apparently wishes 

 to discard the term heliotropism altogether in 

 favour of phototaxis ; but there are certain cases 

 which oppose this blending of terms. 



The nocturnal lepidoptera are negatively 

 heliotropic but positively phototactic, being im- 

 pelled by an irresistible attraction to a bright 

 lamp. Amphioxus, the lancelet, is passively 

 heliotropic, but actively phototactic, evincing 

 extreme agitation upon the approach of a lighted 

 candle at night. In the same way fishes are 

 attracted by torchlight at sea, and lighted lamps 

 are placed at the head of fish -traps, where they 

 are kept burning all night to attract prawns 

 which are required for bait in large quantities. 

 Lighted prawn-traps and moth-traps represent 

 practical applications of the knowledge of the 

 phototactic properties of these animals. The 

 phosphorescent organs of deep-sea fishes no 

 doubt also act as luminous lures. 



An intimate acquaintance with the habits 

 and reactions of animals is not confined to the 

 human race. Many reptiles, birds, and mammals 

 are accomplished field entomologists, know- 

 ing where to look for their food, and how to 

 distinguish edible from inedible kinds. The 



B 2 



