Protorthoptera, ancestors of the Orthoptera, or locusts, etc. Nearly all these insects attained a considerable size; indeed, there were many the span of whose wings measured much more than half a meter—they were literally giants!
These forms, too, decrease in number, and at last there appears to us a quite distinct fauna of primitive creatures, whose structure was of the simplest order, and who were apparently without adaptation to the definite modes of life which we are accustomed to see in nearly all existing insects. These primitive forms we call 'Palæodictyoptera,' and among them it is possible to distinguish a series of different genera and species, all, however, having common characters and standing in about the same degree of relationship to existing groups.
These palæodictyopteres, therefore, constitute the first shoot of the giant tree which we have to-day in the insect world.
As has been frequently indicated, we also see that the race of insects has by no means remained unaltered since primitive times, but that it has been subjected to precisely the same changes as have other groups of animals. And the conclusions to be drawn from these mutations are manifold. In the first place, they permit us to erect a natural system in accordance with actual descent; they permit us to weigh the characters accurately and to distinguish between those which are old and inherited and those that are recent and acquired. Moreover, they afford us many and far-reaching conclusions regarding the climate and the nature of the soil in those times and regions, as well as the distribution of land and water, etc. Finally, by this means we are also enabled to penetrate a very little into the future. And this further shows us that eventually neither the boy with the green net nor the imprecating pessimist will be so very far wrong, for the immediate future probably belongs to the brilliantly colored insects, on the one hand, and, on the other, to the troublesome and offensive vermin, the parasites of man, animals and plants. These two extremes appear to us to-day in their greatest development.