MILLIPEDE, an animal with a dis tinct head, one pair of feelers (antennae) and a segmented body not divided up into regions like that of most arthropods. Each typical segment of the body is provided with two pairs of walking legs (fig. 5). The millipedes form in the phylum Arthropoda the distinct class Diplopoda.
Millipedes have a world-wide distribution, and were among the earliest creatures to emerge from the wa ter, for fossil Diplopoda are known in con siderable numbers from the Devonian and some remains (Archidesmus loganensis) have been found in Scotland even in the Upper Silurian. By Carboniferous times millipedes were well established and are represented by a great array of specimens obtained in the United States, Great Britain and Bohemia. Early millipedes were remarkably like living forms. Some Carboniferous forms were probably amphibious (fig. 8).
The nesting habits of some millipedes are most interesting and somewhat complicated. In Polydesmus the female selects a suit able site on a fragment of wood or a similar object in a damp spot and builds a circular wall by the discharge of faeces, which are moulded by the anal valves ; this process is carried on until the beehive-like nest is well advanced and then the eggs are deposited and the nest is roofed in. The fe
male remains coiled around the nest for some time after the structure is complete (fig. 9).
Skin-changing is a serious dan ger to the life of a millipede because it leaves the animal in an unusually defenceless condition; for this reason the animal goes into retirement when the process is imminent, and in some cases, as in Glosneris and Oxydesmus, a special changing-cell like a nest is constructed.
For some unexplained reason millipedes occasionally move in large numbers, sometimes even in broad daylight. On one occa sion in Alsace a train was stopped because the dead and crushed bodies of the migrating diplopods made the rails slippery.
Some millipedes injure crops, but their masticatory organs are weak and they can only damage delicate tissues such as young roots or internal structures exposed by the attacks of other pests; others eat any decaying tissues.