Leucocytes are known as white blood cells (WBC). They are oval/rounded or irregular in shape. WBCs have nuclei but are devoid of haemoglobin. They are of two kinds : (1) granulocytes, and (2) agranulocytes. Granulocytes possess granules of varying sizes and have lobed nudei. They are of three kinds : (1) basophils, (2) addophils, (3) neutrophils based on the staining feature. Monocytes and lymphocytes are two types of agranulocytes. They are non-granular and always have only one nuclei in individual cell.