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.
Stroma is everything else -- connective tissue, blood vessels, nerves, ducts. The parenchyma / stroma distinction provides a convenient way to circumvent the listing of tissue types when discussing an organ. Examples: 1  The parenchyma of the kidney is epithelial tissue (renal tubules and corpuscles).2  The blood vessels, nerves, and supporting connective tissue of the kidney comprise the stroma. 3  The parenchyma of the spleen is connective tissue (mostly lymphocytes and other blood cells).troma is everything else -- connective tissue, blood vessels, nerves, ducts. The parenchyma / stroma distinction provides a convenient way to circumvent the listing of tissue types when discussing an organ. Examples: 1  The parenchyma of the kidney is epithelial tissue (renal tubules and corpuscles).