Scientists have invented a device that can quickly produce large numbers of living entities that resemble very primitive human embryos.Researchers welcomed the development, described Wednesday in the journal Nature, as an important advance for studying the earliest days of human embryonic development. But it also raises questions about where to draw the line in manufacturing "synthetic" human life.Other scientists have previously created synthetic embryos, which are also known as embryoids. These entities are made by coaxing human stem cells to form structures found in very early human embryos. The research has raised questions about how similar to complete embryos they could and should be...