There are many amazing underground creatures. The stars of the underground show are earthworms, ＿＿（16）＿＿ their role in building soil, their importance to gardeners, and the fascination they afford schoolchildren. Earthworms are giants compared with most other soil ＿＿（17）＿＿ . The earthworm's body is made of ＿＿（18）＿＿ cylinders, which look like many little rings joined together. They are ＿＿（19）＿＿ that chew their way through soil, feeding on plant and animal detritus and on microbes, digesting and thoroughly mixing organic and inorganic components before eliminating it as humus. This ＿＿（20）＿＿ breaks complex organic molecules down into simpler forms more suitable for uptake by plants.