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 insects, the
Orthoptera[5], characterised by firm forewings and biting jaws; in all
of them the change of form during the life-history is comparatively
slight. A great contrast to those insects in the structure of the