Earthworms are lower annelids, although they also have a head, a tail, a mouth, a stomach and an anus. But its whole body is like two sharp "tubes" nested together. The outer layer is the annular body wall, and there is a muscle system composed of mesodermal cells. The body is the digestive tract, which runs through layers of membranes from beginning to end. Between the two "tubes" inside and outside, it is filled with body cavity fluid.
When the earthworm is cut into two sections, under the conditions of temperature, pH and sterilization, the muscle tissue on the section immediately contracts, and some muscles quickly dissolve themselves to form new cell clusters. At the same time, white blood cells gather on the section to form embolism, which makes the wound close quickly. The primary cells located in the septum of body cavity quickly migrate to the slice and form nodular regeneration buds on the slice together with their dissolved muscle cells. At the same time, the cells of digestive tract, nervous system, blood vessels and other tissues in the body quickly grow into regenerated buds through a large number of mitosis. In this way, with the continuous proliferation of cells, a new head will grow on the section lacking the head; The tail will grow on the part where the tail is missing. So one earthworm becomes two complete earthworms.