of an "if" and a "suppose," there is little
difficulty in explaining anything.

The occasional habit of birds laying their
eggs in other birds' nests, either of the same
or of a distinct species, is not very uncommon
with the Gallinaceae; it is frequent with
domestic hens; and this, perhaps, explains the
origin of a singular instinct in the allied group
of ostriches, for several hen ostriches, at least
in the case of the American species, unite and lay,
first a few eggs in one nest, and then the rest 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 in the case of the cuckoo, at
intervals of two or three days. The instinct,
however, of the American ostrich has not as
yet been perfected; for a surprising number of
eggs lie strewed over the plains, so that in one
day's hunting Mr. Darwin himself picked up no
less than twenty lost and wasted eggs.

Many bees are parasitic, and always lay their
eggs in the nests of bees of other kinds. This
case is more remarkable than that of the
cuckoo, for these bees have not only their
instincts, but their structure also, modified in
accordance with their parasitic habits: they do
not possess the pollen-collecting apparatus
which would be necessary if they had to store
food for their own young. Some species likewise
of Sphegidae (wasp-like insects) are parasitic
on other species; and M. Fabre has lately
shown good reason for believing that although
the Tachytes nigia generally makes its own
burrow and stores it with paralysed prey for its
own larvae to feed on, 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 the supposed case of the cuckoo, Mr.
Darwin 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 thus feloniously
appropriated, be not thus exterminated.

Such ideas are opposed to the belief of
philosophers who hold that the various species of plants
and animals have been independently created, and
have been purposely fitted and adapted to the
place in creation which they were intended to
occupy by an Overruling Intelligence; for it is
maintained that the more complex organs and
instincts have been perfected, not at once in the
first-created individual, by the Hand of the
Maker, but by the accumulation of innumerable
slight variations, each good for the individual
possessor for the time being, during an exceedingly
long succession of individuals from generation
to generation.

The result is asserted to have been effected in
this way: there can be no doubt that species
give rise to minor varieties; for no two
individuals are exactly alike, but may be easily
distinguished one from the other. A shepherd
knows every sheep in his flock, a huntsman every
hound in his pack, calling it by name; a busy-
body knows every face in his village and its
neighbourhood; probably a bee knows every
bee belonging to its hive. Variations are often
hereditary; red-haired parents will probably
have a red-haired family. Varieties of talent
and bodily strength are hereditary; diseases
and defects are hereditary, as is every day seen
with consumption and deafness. If any animal
or plant in a state of nature be highly useful to
man, or from any cause closely attract his attention,
varieties of it will almost universally be
found recorded. Now, individual differences
are considered by Mr. Darwin as the first step
towards such slight varieties as are barely
thought worth mentioning in works on natural
history: varieties which are in any degree more
distinct and permanent, are steps leading to
more strongly marked and more permanent
varieties; and these latter lead to sub-species,
and to species. In short, all organised and
animated forms are in a state of passage from
one stage of difference to another; all nature is
moving insensibly forwards up the slope of one
vast sliding scale; the world is a never-ceasing
workshop for the process of manufacturing new
species of plants and animals.

Mr. Darwin believes that any well-marked
variety may be called an incipient species; and
herein lies the whole turning-point, the cornerstone,
perhaps the stumbling-block, of his System
of Nature; grant him that, and nothing can
stop the career of his theory; give him that
inch, and he may take, not an ell, but a hundred
thousand miles of philosophical territory.
Conscious of the importance of his postulate, he
candidly observes: " Whether this belief" (that
varieties are incipient species) " be justifiable,
must be judged of by the general weight of the
several facts and views given throughout this
work." Achilles is a mighty man, but unfortunately
he is afflicted with a vulnerable heel.
Elsewhere he says: " It has often been asserted,
but the assertion is quite incapable of proof,
that the amount of variation under nature is a
strictly limited quantity." But there's the rub.
A mathematical demonstration may be impossible;
but certain observers and experimenters
say that their experiments and observations
strongly tend to the belief that varieties do not
vary beyond certain limits; that is the impression
which their minds receive from what they
see; just as Mr. Darwin's observations strongly
tend to make him view all existing beings, not
as special creations, but as the lineal descendants
of some few beings which lived long before the
first bed of the Silurian system was deposited,
and to conclude thence that (as all the living
forms of life are the lineal descendants of those
which lived long before the Silurian epoch) we
may feel certain that the ordinary succession by
generation has never once been broken, that no
cataclysm has desolated the whole world, and
that we may look with some confidence to a
secure future of equally inappreciable length.

But no human intellect, unaided by revelation,
is at present able to make such conclusions as
these matters either of positive proof or of
positive refutation. They must remain a question