In at least one species of skink in the large genus "Trachylepis", placental transport accounts for nearly all of the provisioning of nutrients to the embryos before birth. In the uterus, the eggs are very small, about 1 mm in diameter, with very little yolk and very thin shells. The shell membrane is vestigial and transient; its disintegration permits the absorption of nutrients from uterine secretions. The embryo then produces invasive chorionic tissues that grow between the cells of the uterine lining till they can absorb nutrients from maternal blood vessels. As it penetrates the lining, the embryonic tissue grows aggressively till it forms sheets of tissue beneath the uterine epithelium. They eventually strip it away and replace it, making direct contact with maternal capillaries. In several respects, the phenomenon is of considerable importance in theoretical zoology. Blackburn & Flemming (2011) remark that such an endotheliochorial placenta is fundamentally different from that of any known viviparous reptile.