This, as already explained, is the embryonic or ontogenic series.
Because we can trace the change from the one to the other in the ontogenic series.
But there is another essential element in ontogenic evolution.
This ontogenic fact is supremely important, for the most far-reaching conclusions may be drawn from it.
ontogeny on·tog·e·ny (ŏn-tŏj'ə-nē)
The origin and development of an individual organism from embryo to adult. Also called ontogenesis.