51.   This would halt research at a point when the embryo is a tiny formless mass of cells with no developed nervous system.

52.   Today, the debate centers on whether embryos should be viewed as viable human beings or a cluster of cells smaller than the naked eye can see.

53.   To him, three or four embryos would be an acceptable guideline.

54.   Typically, three embryos are implanted.

55.   Two of those split embryos will be identical twins if they survive until birth, which is expected in May.

56.   Up to six days after fertilization, the embryo is a tiny white opalescent cylinder, still far more like an egg than an animal.

57.   Opponents say a cloned embryo is a human being and that manufacturing it is unethical.

58.   Our pictures show the labs where the embryos are stored, and comment from a scientist, a pro-life campaigner and a donor mother.

59.   But the fact that an embryo was grown for six weeks in a surrogate instead of a test tube concerned even some therapeutic cloning proponents.

60.   But the research is opposed by many who believe an embryo is a life and that destroying it for any reason is wrong.