Inverse prominence of ependyma and capillaries in the spinal cord of vertebrates: a comparative histochemical study

Spinal cords of 15 species representing six classes of vertebrates and the protochordate amphioxus were examined with histochemical methods for esterase, ATPase, LDH, PAS, and PAS-phosphorylase. Ependymal and glial cell processes were demonstrated and resembled heavy metal impregnations. Capillaries also were shown. The prominence of glycogen-rich ependymal structures in the spinal cord of nonmammalian vertebrates, and the increase in intramedullary blood vessels in placental mammals, suggest an inverse relationship between the relative development of the ependyma and of the blood supply. The marsupial opossum has sparseness of both ependyma and capillaries, but exhibits an extensive pattern of branched glial processes in both white and gray matter.