aboriginal instinct of nidification.

It has been objected that I have not noticed other related instincts and
adaptations of structure in the cuckoo, which are spoken of as necessarily
co-ordinated. But in all cases, speculation on an instinct known to us
only in a single species, is useless, for we have hitherto had no facts to
guide us. Until recently the instincts of the European and of the non-
parasitic American cuckoo alone were known; now, owing to Mr. Ramsay's
observations, we have learned something about three Australian species,
which lay their eggs in other birds' nests. The chief points to be
referred to are three: first, that the common cuckoo, with rare
exceptions, lays only one egg in a nest, so that the large and voracious
young bird receives ample food. Secondly, that the eggs are remarkably
small, not exceeding those of the skylark--a bird about one-fourth as large
as the cuckoo. That the small size of the egg is a real case of adaptation
we may infer from the fact of the mon-parasitic American cuckoo laying
full-sized eggs. Thirdly, that the young cuckoo, soon after birth, has the
instinct, the strength and a properly shaped back for ejecting its foster-
brothers, which then perish from cold and hunger. This has been boldly
called a beneficent arrangement, in order that the young cuckoo may get
sufficient food, and that its foster-brothers may perish before they had
acquired much feeling!

Turning now to the Australian species: though these birds generally lay
only one egg in a nest, it is not rare to find two and even three eggs in
the same nest. In the bronze cuckoo the eggs vary greatly in size, from
eight to ten lines in length. Now, if it had been of an advantage to this
species to have laid eggs even smaller than those now laid, so as to have
deceived certain foster-parents, or, as is more probable, to have been
hatched within a shorter period (for it is asserted that there is a