Waaaay back in 1976, I was sittting it my AP Biology class, and the teacher wrote the phrase "Ontogeny recapitulates phylogeny" on the board. We were all told to memorize it, but it was never explained. (We were dissecting a fetal pig and also learning the genus & species names of the common flora around the school at the time {Acer rubrum, anyone?}, but other than that, I don't know how the phrase related to what we were studying.
Of course I looked it up, now that we have this wonderful machine at our fingertips, but all I get are entries like "embryological law", "biological paradigm",...and I'm still pretty much as clueless as I was when I was 17. Anyone willing to explain what it is/was? Was it a big secret or something? Was he teaching us something that might be frowned upon by some, like....evolution?