ABSTRACT
Even though blood can be considered a type of connective tissue, its greater specialisation makes it have a dedicated chapter together with the organ where the blood cells are produced: the bone marrow. In this chapter, the different blood cell populations (erythrocytes, leukocytes, and platelets) and the comparative cytology among mammalian, avian, amphibian, and reptilian species are described. The description of the bone marrow microscopic appearance is accompanied by the process of how blood cells are produced (haematopoiesis).
