al segment, and a
pair of unjointed limbs or stylets on the ninth. In the adult stage,
both sexes possess cercopods, but the males only have stylets, those of
the female disappearing at the final moult.

Reviewing the main features of the life-story of a grasshopper or
cockroach, we notice that there is no marked or sudden change of form.
The newly-hatched insect resembles generally its parent, except that it
has no wings. Wing-rudiments appear, however, in an early instar as
visible outgrowths on the thoracic segments, and become larger after
each moult. All through its various stages the immature insect--_nymph_
as it is called--lives in the same kind of situations and on the same
kind of food as its parent, and it is all along active and lively,
undergoing no resting period like the pupal stage in the transformation
of the butterfly.

One interesting and suggestive fact remains to be mentioned. There are
grasshoppers and cockroaches in which the changes are even less than
those just sketched, because the wings remain, even in the adult, in a
rudimentary state (as for example in the female of the common kitchen
cockroach, _Blatta orientalis_, see fig. 4 _a_), or are never developed
at all. Such exceptional winglessness in members of a winged family can
only be explained by the recognition of a life-story, not merely in the
individual but in the race. We cannot doubt that the ancestors of these
wingless insects possessed wings, which in the course of time have been
lost by the whole species or by the members of the female sex. It is
generally assumed that this loss has been gradual, and so in many cases
it probably may have been. But there are species of insects in which
some generations are winged and others wingless; a winged mother gives
birth to wingless offspring, and a wingless parent to young with
well-developed wings. Such discontinuity in the life-story of a single
generation forces us to recognise the possibility of similar sudden
mutations in the course of that age-long process of evolution to which
the facts of insect growth, and indeed of all animal development, bear
striking testimony.

CHAPTER III

THE LIFE-STORIES OF SOME SUCKING INSECTS

We may now turn our attention to some examples of the remarkable
alternation of winged and wingless generations in the yearly life-cycle
of the same species, mentioned at the end of the last chapter.
Cockroaches and grasshoppers belong to an order of inse