years of discretion.

[Illustration: SEA-HORSES.]

Without taking into account insects and such other "small deer,"--to
quote Shakespeare's expression,--this fundamental principle of
population will become at once apparent if we examine merely familiar
instances of back-boned or vertebrate animals. The lowest vertebrates
are clearly the fishes: and the true fishes have almost invariably
gigantic families. A single cod, for example, is said to produce,
roughly speaking, nine million eggs at a birth (I cannot pretend I
have checked this calculation); but supposing they were only a
million, and that one-tenth of those eggs alone ever came to maturity,
there would still be a hundred thousand codfish in the sea this year
for every pair that swam in it last year: and these would increase to
a hundred thousand times that number next year; and so on, till in
four or five years' time the whole sea would be but one solid mass of
closely-packed cod-banks. We can see for ourselves that nothing of the
sort actually occurs--practically speaking, there are about the same
number of cod one year as another. In spite of this enormous
birth-rate, therefore, the cod population is not increasing--it is at
a standstill. What does that imply? Why, that taking one brood and one
year with another, only a pair of cod, roughly speaking, survive to
maturity out of each eight or nine million eggs. The mother cod lays
its millions, in order that two may arrive at the period of spawning.
All the rest get devoured as eggs, or snapped up as young fry, or else
die of starvation, or are otherwise unaccounted for. It seems to us a
wasteful way of replenishing the earth: but it is nature's way; we can
only bow respectfully to her final decision.