48 HOUSE, GARDEN, AND FIELD 



in different parts of the world. Some centipedes, one of 

 which is common in Britain, have the same property. 

 Many inhabitants of the sea are luminous, among the 

 rest, deep-sea fishes, mollusks, crustaceans, worms, echino- 

 derms and zoophytes. A protozoan not more than one- 

 fiftieth of an inch long causes what we describe as the 

 phosphorescence of the sea. 



There are also light- emitting plants. The threads of 

 certain fungi which subsist upon decaying wood shine in 

 the dark ; so do the bacteria which set up putrefaction in 

 the bodies of dead marine-fishes. Observant persons are 

 familiar with both kinds of luminosity. In fish-cleaning 

 yards, especially such as are regularly overflowed by the 

 tide, luminosity can often be remarked. I have seen 

 hastily cleaned fishes' skulls shine every night for weeks. 

 If .they are washed with water, the water may become 

 luminous ; when filtered, the water loses its power of 

 emitting light, but the filter begins to shine. 



Flowers have occasionally been seen to emit flashes of 

 light, but these are due to causes of another kind. 



QUESTION 3. What benefit do the glowworms derive from 

 their power of emitting light ? 



Gilbert White's explanation that the light of the glow- 

 worm is attractive to the male insect seems to be a little 

 too ancient for some biologists, who are restless until they 

 can replace it by a theory more worthy, as they think, of 

 the twentieth century. But the old view makes intel- 

 ligible several facts that must never be lost sight of. 

 Bongardt has recently placed on record the important 

 observation that a female glowworm when exposed in a 

 bottle brings around a number of faintly illuminated 

 males, and at their approach her light becomes more 

 vivid. In our common English glowworm the female, 

 which is pre-eminently luminous, has no wings, and the 

 winged male has particularly large eyes. The same cannot 

 be said of all glowworms, and hence a doubt has arisen. 



