Parasite survival depends on transmitting from one host to the next, sometimes through an intermediate species.

寄生虫的生存取决於从 这个宿主传送到另一个宿主的过程，有时会通过不同种的宿主。

The intermediate species, also (and this is a very important consideration), which connected the original species (A) and (I), have all become, except (F), extinct, and have left no descendants.

连接原始物种（A）和（I）的中间物种（这是一个非常重要的考虑因素），除了（F）外， 都已经灭绝， 并且没有留下后代。