Nearly a century ago, biologists found that if they separated an invertebrate animal embryo into two parts at an early stage of its life, it would survive and develop as two normal embryos.

• 近一个世纪以前，生物学家发现，如果他们将一个在其生命早期的非脊椎动物胚胎一分为二，胚胎会存活并发育成两个正常的胚胎。