I explain it on two grounds, I replied. In the first place, because vertical currents, which are caused by differences in the water's salinity and density, can produce enough motion to sustain the rudimentary lifestyles of sea lilies and starfish.

我用两个理由来解释，我回答，第一，因为那些上下垂直往来的水流，由海水的不同咸度和不同密度决定，发生一种运动，足以维持海百合和海星一类的原始基本生活。