拖动鼠标到未加下划线的蓝色字体上，出现附加注释框。点击加下划线的蓝色字体(例如多数图例后的三个圆点), 注释框停留在屏幕上。移开鼠标到未加下划线的图例上，则注释框消失。试一试吧，非常简单！
Mitochondria are producing energy in the cell. They have a double membrane; the
outer one is very permeable, while the inner membrane bears invaginations called
cristae which contain chains on enzymes involved in the respiratory chain of metabolism.
Mitochondria are producing energy in the cell. They most probably originated
from ancient prokaryotic cells which were able to perform oxidative metabolism.
They were engulfed by the predecessors of eukaryotic cells incapable of oxidative
metabolism. So it is believed that the outer mitochondrial originates from
the eukaryotic cell while the inner mitochondrial membrane originates from
the prokaryotic cell. The outer membrane is very permeable, while the inner
membrane bears invaginations called cristae which contain chains on enzymes
involved in the respiratory chain of metabolism.
