ely they may have come
under the notice of entomologists. "A very strong argument for the
possibility of some flying insects being occasionally luminous (in
England) is afforded by the facts ... of luminous caterpillars having
been within these few years observed for the first time since entomology
has been attended to, and that by observers every way competent. If
caterpillars so very common as those of _Mamestra oleracea_ may
sometimes, though so rarely, be luminous, and if, as Dr Boisduval
suggests, and is very probable, this appearance was caused by disease,
it is obvious that flying insects may be also occasionally (though
seldom) luminous from disease--a supposition which will at once explain
the rarity of the occurrence, and the circumstance that insects of such
different genera, and even orders, are said to have exhibited this
phenomenon."[156]

These highly curious facts should make observers cautious in strongly
denying statements made by others of phenomena, when they themselves
have not been so fortunate as to witness them, even though they may
think their opportunities to have been as favourable as those of the
_soi-disant_ observer.[157]

But we have not yet dismissed Madame Merian. If acquitted of falsehood
here, she stands arraigned on a second charge of similar character.

In most tropical countries there are found hideous hairy spiders of
monstrous size and most repulsive appearance; short-legged, sombre-hued,
ferocious marauders of the night, that by day lurk in obscure retreats
under stones, or in burrows in the earth.

Guiana produces a formidable species of this sort (_Mygale avicularia_),
which measures three inches in length, and whose feet--though the genus
is, as I have said, comparatively short-limbed--cover an area some
eight or ten inches in diameter. Madame Merian has exquisitely figured
the tragical end of a tiny humming-bird, surprised by one of these
monsters on her eggs; the petite bird overthrown under the fangs of the
sprawling spider, one of whose feet is in the nest. It was on the
authority of this lady that Linnaeus gave the name of _avicularia_ to the
species. Later naturalists have scouted the whole story. Mr MacLeay, who
resided in Cuba, says that there are indeed there huge spiders, allied
to our garden spider, which make a geometric net, strong enough to
embarrass small birds; but that these do not attempt to catch such prey,
and never molest birds at all. On the other han