The Development of the Animal World 75 



properly in the Ordovician) strata. In the Devonian we 

 have fairly abundant traces of insects. They are unlike 

 any modern type, and have the general characters that 

 we look for in the ancestors of divergent families. In 

 the luxuriant vegetation of the Carboniferous we 

 naturally find large numbers of fresh species. They are 

 mostly of the Orthoptera (cockroaches, locusts, etc.) or 

 Neuroptera (may-flies) types, and we find no specimens 

 as yet of the Hymenoptera (ants, bees, etc.), Lepidoptera 

 (butterflies), or Diptera (house-fly, gnat, etc.). In the 

 Triassic period the Coleoptera appear, and in the 

 Jurassic we find the first Hymenoptera — the highest 

 order. By the beginning of the Tertiary all orders are 

 definitely and abundantly represented. Even now, 

 however, the ants — of which there are more than a 

 hundred species — do not seem to have evolved a social 

 life. All are winged, so that the remarkable organisation 

 into male, female, and neuter, cannot yet have set in. 



These geological indications, taken together with the 

 metamorphosis of the insect, give us ample guarantee of 

 the evolution of the insect world. We must, however, 

 retrace our steps a little, and return to the pre-Cambrian 

 ocean with all its ancestral types, in order to take up 

 the thread of the evolution of the vertebrates, which will 

 soon lead us to firmer ground. Once a bony framework 

 is set up in the animal, fossilisation becomes easy, and 

 our task is proportionately easier. 



That the fish was developed from some one of those 

 early worm-like creatures in the pre-Cambrian ocean is 

 the almost universal opinion of geologists and zoologists. 

 A few, it is true, are inclined to look to the Ostracoderms 

 for the vertebrate ancestor. In earlier geological works 

 the reader will find illustrations of what are called 

 M upper Silurian fishes " (CepJialaspis, Pteraspis, etc.) — 

 heavily-armoured creatures of a fish-like character. 



