Members of the family Dasyatidae, like other rays and their shark relatives, employ a reproductive strategy that involves putting a great investment of energy into relatively few young over a lifetime. Once sexually mature, stingrays have only one litter per year, usually bearing two to six young. Since few young are produced, it is important that they survive, and to this end rays are born at a large size, able to feed and fend for themselves much like an adult. Rays develop from egg to juvenile inside the mother’s uterus, sometimes to almost half their adult size. In this system, called aplacental uterine viviparity, developing embryos receive most of their nutriment from a milky, organically rich substance secreted by the mother’s uterine lining. An embryo absorbs this substance, called histotroph, by ingestion, or through its skin or other specialized structures. Researchers have found that in some stingrays, the stomach and spiral intestine are among the first organs to develop and function, so that the embryo can digest the uterine “milk.” Rays’ eggs are small and insufficient to support the embryos until they are born, although the first stage of development does happen inside tertiary egg envelopes that enclose each egg along with egg jelly. The embryo eventually absorbs the yolk sac and stalk and the histotroph provides it with nutrition. Embryos are so well nourished in the uterus that in Dasyatis americana, for example, the young ray’s net weight increases by 3750% from egg to birth. Development in the uterus usually takes about two to four months. At birth the ray is fully developed and looks like a small adult.