Formation of brown bodies in the coelomic cavity of the earthworm Eisenia fetida andrei and attendant changes in shape and adhesive capacity of constitutive cells.

The formation of brown bodies in the coelomic cavity may result from an aggregation of coelomocytes around offending foreign cells such as bacteria, gregarines, incompatible graft fragments, and altered self structures such as setae or necrotic muscle cells. The initial nodule rapidly increases in volume by aggregation of new coelomocytes and various waste particles. When a brown body has reached a diameter of 1-2 mm, its external cells flatten and lose their adhesiveness toward free coelomocytes or waste particles and its pigment rapidly darkens. Brown bodies play an important role in homeostasis.