51.   Still, some scientists acknowledge that in human embryonic cell work, many nontrivial technical obstacles remain to be overcome.

52.   The ability of the embryonic cells to grow into an infant cannot at present be determined.

53.   That is when an unfertilized egg cell is fooled, with chemicals, into developing early embryonic cells as if it were actually fertilized.

54.   The abortion foes accused Bush of breaking a campaign promise to outlaw research on living embryonic cells, a pledge he reiterated to an anti-abortion group in May.

55.   The agency says it will make a registry of human embryonic cell lines available on its Web site as soon as possible.

56.   The birth defects occur when a sheath of embryonic cells fails to close completely to form the spinal cord and brain during the first month of pregnancy.

57.   The emerging picture is that teeth develop through genetically signaled interactions between two sheets of embryonic cells, known as the epithelium and the mesenchyme.

58.   The debate on research involving embryonic cells, also known as stem cells, has divided the administration publicly, and sharply.

59.   The developing nervous system is a fluid-filled cavity or tube surrounded by embryonic cells.

60.   The germ cells are set aside at an early stage and protected from the maturing process that affects all the other embryonic cells.