TEM of red blood corpuscles and lymphocytes in splenic sinuses. A blood cell, also called a haematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Red blood cells (RBCs), also called erythrocytes, are the most common type of blood cell and the vertebrate organism's principal means of delivering oxygen (O2) to the body tissues- via blood flow through the circulatory system. A lymphocyte is one of the subtypes of white blood cell in a vertebrate's immune system. The red pulp of the spleen is composed of connective tissue known as the cords of Billroth and many splenic sinuses that are engorged with blood, giving it a red color. Magnification @ 19,000x, 8x10 Print.