ABSTRACT
The red blood cells of birds appear elliptical in outline and have elliptical nuclei, whereas those of reptiles and amphibians have more rounded ends and the nuclei are usually round. Deep sea teleosts have larger size red blood cells than normal teleosts. Small red blood cells are found in species which normally live at high altitudes. Rouleaux formation is confined to discoid red blood cells and does not occur in camelids, birds, reptiles, amphibians and fish. The latter is characterised by a close, irregular juxtaposition of red blood cells into clumps of various sizes, indicating an abnormal immune response, and is never seen under normal circumstances. In some species, the presence of intra-erythrocytic haemoglobin crystals can disrupt the spreading of a blood film in such a way that the red blood cells appear to be agglutinated. Since the mean cell haemoglobin concentration is similar in all mammals and birds, mammalian and avian red blood cells normally should appear fully haemoglobinised.
