Anus vs. Mouth

Protostomes and Deuterostomes: a real dumb way to classify animals. Maybe developmental biologists can tell the difference between an organism whose first hole becomes a mouth, and an organism whose first hole becomes an anus - but I sure can’t. Though, now that I think about it, this confusion might just be responsible for every single imperfection in my life so far.

And in case you’re curious, humans are deuterostomes - our initial embryonic opening develops into an anus. We share this characteristic with all other chordates, and also echinoderms. That is why there are always more horses’ asses than there are horses.