The species theory, polygenism, held that human races were of different lineages and suggested a hierarchy outlined in the Chain of Being that positioned Africans between man and lower primates.
No, they are involved in the Circulatory System which is responsible for pumping and channelling blood to and from the body and lungs with heart, blood and blood vessels. no veins are not considered an organ because they are a grouping of different tissues like a organ.
Tissue fluid is similar to blood, but doesnât contain most of the cells found in blood, nor does it contain plasma proteins. The role of tissue fluid is to transport and nutrients from the blood to the cells, and to carry carbon dioxide and other. wastes back to the blood. When an artery reaches the tissues it branches out into smaller. arterioles, then into a network of capillaries which eventually link up.