the stranger. They either lay their eggs in the nest
thus appropriated, or oddly enough build one for themselves on the top
of it. They usually sit on their own eggs and rear their own young; but
Mr. Hudson says it is probable that they are occasionally parasitic, for
he has seen the young of this species following old birds of a distinct
kind and clamouring to be fed by them. The parasitic habits of another
species of Molothrus, the M. bonariensis, are much more highly developed
than those of the last, but are still far from perfect. This bird, as
far as it is known, invariably lays its eggs in the nests of strangers;
but it is remarkable that several together sometimes commence to build
an irregular untidy nest of their own, placed in singular ill-adapted
situations, as on the leaves of a large thistle. They never, however, as
far as Mr. Hudson has ascertained, complete a nest for themselves. They
often lay so many eggs--from fifteen to twenty--in the same foster-nest,
that few or none can possibly be hatched. They have, moreover, the
extraordinary habit of pecking holes in the eggs, whether of their own
species or of their foster parents, which they find in the appropriated
nests. They drop also many eggs on the bare ground, which are thus
wasted. A third species, the M. pecoris of North America, has acquired
instincts as perfect as those of the cuckoo, for it never lays more than
one egg in a foster-nest, so that the young bird is securely reared. Mr.
Hudson is a strong disbeliever in evolution, but he appears to have been
so much struck by the imperfect instincts of the Molothrus bonariensis
that he quotes my words, and asks, "Must we consider these habits, not
as especially endowed or created instincts, but as small consequences of
one general law, namely, transition?"

Various birds, as has already been remarked, occasionally lay their eggs
in the nests of other birds. This habit is not very uncommon with the
Gallinaceae, and throws some light on the singular instinct of the
ostrich. In this family several hen birds unite and lay first a few eggs
in one nest and then in another; and these are hatched by the males.
This instinct may probably be accounted for by the fact of the hens
laying a large number of eggs, but, as with the cuckoo, at intervals of
two or three days. The instinct, however, of the American ostrich, as
in the case of the Molothrus bonariensis, has not as yet been perfected;
for a surprising numbe