to chrysalis and butterfly. After the fourth moult,
the young aphides attain maturity; and then they give origin,
parthenogenetically, to a second brood, also of imperfect females, all
produced without any fathers. This second brood brings forth in like
manner a third generation, asexual, as before; and the same process is
repeated without intermission as long as the warm weather lasts. In each
case, the young simply bud out from the ovaries of the mothers, exactly
as new crops of leaves bud out from the rose-branch on which they grow.
Eleven generations have thus been observed to follow one another rapidly
in a single summer; and indeed, by keeping the aphides in a warm room,
one may even make them continue their reproduction in this purely
vegetative fashion for as many as four years running. But as soon as
the cold weather begins to set in, perfect male and female insects are
produced by the last swarm of parthenogenetic mothers; and these true
females, after being fertilised, lay the eggs which remain through the
winter, and from which the next summer's broods have to begin afresh the
wonderful cycle. Thus, only one generation of aphides, out of ten or
eleven, consists of true males and females: all the rest are false
females, producing young by a process of budding.

Setting aside for the present certain special modifications of this
strange cycle which have been lately described by M. Jules Lichtenstein,
let us consider for a moment what can be the origin and meaning of such
an unusual and curious mode of reproduction.

The aphides are on the whole the most purely inactive and vegetative of
all insects, unless indeed we except a few very debased and degraded
parasites. They fasten themselves early in life on to a particular shoot
of a particular plant; they drink in its juices, digest them, grow, and
undergo their incomplete metamorphoses; they produce new generations
with extraordinary rapidity; and they vegetate, in fact, almost as much
as the plant itself upon which they are living. Their existence is
duller than that of the very dullest cathedral city. They are thus
essentially degenerate creatures: they have found the conditions of life
too easy for them, and they have reverted to something so low and simple
that they are almost plant-like in some of their habits and
peculiarities.

The ancestors of the aphides were free winged insects; and, in certain
stages of their existence, most living species of aphid