172 The Nahtralist 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 ivarn, 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 
