232 DIVERSIONS OF A NATURALIST 



luminous ancestors and a similar early history. This 

 is a legitimate supposition, since there are several very 

 distinct kinds of insects known at the present day which 

 are luminous at night, although no existing moths or 

 butterflies are known to be so. 



A fact bearing on the explanation of the insects' 

 perilous rush to flame is that birds when migrating are 

 attracted by the great brilliant lamps of lighthouses, and, 

 flying towards them, strike against their glass coverings, 

 and are killed in considerable numbers. In that case, 

 it may be that the flying towards the sun has become 

 instinctive, and that the bright Ught of the lighthouse 

 acts upon a certain number of birds (perhaps the less 

 well-adjusted individuals) so as to call forth the same 

 response in the direction of flight as that exercised by 

 the sun's globe. The truth or error of this suggestion 

 should be tested by an examination of the species of 

 birds which kill themselves against lighthouse lanterns, 

 and a knowledge of the season and direction of their 

 migration. 



As to luminous or phosphorescent (often called 

 " luminescent ") insects and other animals, there are a 

 great many curious and interesting facts known. There 

 are luminescent bacteria (common on old meat bones and 

 dead fish and in the sea generally), animalcules of various 

 species, jelly-fish, star-fish, worms, shell-fish, and crus- 

 taceans and true fishes. Inhabitants of the great depths 

 of the ocean of all kinds are usually luminescent. The 

 light is caused by the oxidation of a peculiar fatty 

 substance. Without free oxygen there is no lumin- 

 escence, and yet no heat is produced but merely light, 

 as when a stick of damp phosphorus glows. The lumin- 

 escence of living things (often, but undesirably, called 



