Darwin began work on a series of secret notebooks containing his thoughts about the evolutionary process.

VOA: special.2009.02.25

Well, that process occurs in a series of steps and one of those kinds of steps is shown here.

这个过程的发生包含一系列步骤,而这些步骤中的一个步骤即如图所示

耶鲁公开课 - 生物医学工程探索课程节选