Abstract
The leucocytes and related cells of the blood of plaice were examined morphologically and their various functions assessed using a number of procedures to identify phagocytosis histochemical reactions and antibody responses. Four morphologically different types of thrombocytes were identified in addition to lymphocytes, plasma cells, monocytes, macrophages and one type of granulocyte which histochemically resembled the mammalian neutrophil. The evolution and development of the cells was also investigated and the various stages described.