In Peripatus we have a strange survivor of these primitive Annelid-Tracheates of many million years ago. The simple nature of its breathing apparatus suggests that the trachere were developed out of glands in the skin; just as the fish, when it came on land, probably developed lungs from its swimming bladders. The primitive Tracheates, delivered from the increasing carnivores of the waters, grew into a large and varied family, as all such new types do in favourable surroundings. From them in the course of time were evolved the three great classes of the Myriapods (millipedes and centipedes), the Arachnids (scorpions, spiders, and mites), and the Insects. I will not enter into the much-disputed and Obscure question of their nearer relationship. Some derive the Insects from the Myriapods, some the Myriapods from the Insects, and some think they evolved independently; while the rise of the spiders and scorpions is even more obscure. But how can we see any trace of an Annelid ancestor in the vastly different frames of these animals which are said to descend from it? It is not so difficult as it seems to be at first sight. In the Myriapod we still have the elongated body and successive pairs of legs. In the Arachnid the legs are reduced in number and lengthened, while the various segments of the body are fused in two distinct body-halves, the thorax and the abdomen. In the Insect we have a similar concentration of the primitive long body. The abdomen is composed of a large number (usually nine or ten) of segments which have lost their legs and fused together. In the thorax three segments are still distinctly traceable, with three pairs of legs--now long jointed limbs--as in the caterpillar ancestor; in the Carboniferous insect these three joints in the thorax are particularly clear. In the head four or five segments are fused together. Their limbs have been modified into the jaws or other mouth-appendages, and their separate nerve-centres have combined to form the large ring of nerve-matter round the gullet which represents the brain of the insect.