r of eggs lie strewed over the plains, so that in
one day's hunting I picked up no less than twenty lost and wasted eggs.

Many bees are parasitic, and regularly lay their eggs in the nests
of other kinds of bees. This case is more remarkable than that of the
cuckoo; for these bees have not only had their instincts but their
structure modified in accordance with their parasitic habits; for they
do not possess the pollen-collecting apparatus which would have been
indispensable if they had stored up food for their own young. Some
species of Sphegidae (wasp-like insects) are likewise parasitic; and
M. Fabre has lately shown good reason for believing that, although
the Tachytes nigra generally makes its own burrow and stores it with
paralysed prey for its own larvae, yet that, when this insect finds a
burrow already made and stored by another sphex, it takes advantage of
the prize, and becomes for the occasion parasitic. In this case, as
with that of the Molothrus or cuckoo, I can see no difficulty in natural
selection making an occasional habit permanent, if of advantage to the
species, and if the insect whose nest and stored food are feloniously
appropriated, be not thus exterminated.

SLAVE-MAKING INSTINCT.

This remarkable instinct was first discovered in the Formica (Polyerges)
rufescens by Pierre Huber, a better observer even than his celebrated
father. This ant is absolutely dependent on its slaves; without their
aid, the species would certainly become extinct in a single year. The
males and fertile females do no work of any kind, and the workers or
sterile females, though most energetic and courageous in capturing
slaves, do no other work. They are incapable of making their own nests,
or of feeding their own larvae. When the old nest is found inconvenient,
and they have to migrate, it is the slaves which determine the
migration, and actually carry their masters in their jaws. So utterly
helpless are the masters, that when Huber shut up thirty of them without
a slave, but with plenty of the food which they like best, and with
their larvae and pupae to stimulate them to work, they did nothing; they
could not even feed themselves, and many perished of hunger. Huber then
introduced a single slave (F. fusca), and she instantly set to work, fed
and saved the survivors; made some cells and tended the larvae, and
put all to rights. What can be more extraordinary than these
well-ascertained facts? If we had not known of an