1 72 The Naturalist in La Plata. 



display made by luminous insects is useful only in 

 preventing accidental injuries to them from a few 

 crepuscular bats and goatsuckers. And to believe 

 even this we should first have to assume that bats 

 and goatsuckers are differently constituted from all 

 other creatures; for in other animals — insects, birds, 

 and mammalians — the appearance of fire by night 

 seems to confuse and frighten, but it certainly 

 cannot be said to warn, in the sense in which 

 that word is used when we speak of the brilliant 

 colours of some butterflies, or even of the gestures 

 of some venomous snakes, and of the sounds they 

 emit. 



Thus we can see that, while the old theory of 

 Kirby and Spence had some facts to support it, the 

 one now in vogue is purely fanciful. Until some 

 better suggestion is made, it would perhaps be as 

 well to consider the luminous organ as having " no 

 very close and direct relation to present habits of 

 life." About their present habits, however, especi- 

 ally their crepuscular habits, there is yet much to 

 learn. One thing I have observed in them has 

 always seemed very strange to me. Occasionally an 

 individual insect is seen shining with a very large and 

 steady light, or with a light which very gradually 

 decreases and increases in power, and at such times 

 it is less active than at others, remaining for long 

 intervals motionless on the leaves, or moving with 

 a very slow flight. In South America a firefly dis- 

 playing this abnormal splendour is said to be dying, 

 and it is easy to imagine how such a notion origi- 

 nated. The belief is, however, erroneous, for some- 

 times, on very rare occasions, all the insects in one 



