Thanks, guys. Drawing this page was so much fun, especially after drawing so many pages of houses and yards.
*thinks, "Hrm, why doesn't the amphibian lady have a vagina?"*
*thinks some more, "Wait... do frogs even have vaginas?"*
*subsequently learns a lot about cloacas*
Indirect biology lesson - nice. 
Yay, learning!
Cloacas are weird, but posterior orifices/reproductive systems can get even weirder, even among mammals. Monotremes (platypus and echidna) lay eggs through a cloaca (like the non-mammalian tetrapods: amphibians and reptiles [including birds]), but marsupials have
crazy junk going on down there. Like, three vaginal canals and stuff like that. Even among placentals (mammals that aren't monotremes or marsupials), there's quite a bit of vaginal/clitoral variation. One of my favorite things that I learned about just this past year or so has been the
spotted hyena clit. It's craaazy. I knew that they had false penises before, and that the females are the dominant sex, but I had no idea that these giant clit-dongs were what these creatures got boned in, peed out of, and gave birth through, among a zillion other wacky factoids. I've actually been wanting to make an infographic about spotted hyenas for a while now. Maybe I'll get around to it someday. Why don't they teach us these things in school??

Anyway, the teal alien also has tits, and is pretty anthropomorphic, so anatomical accuracy is sort of out the window. She's an alien, so whatever. I thought about turning her big cheeks into tits too, with multiple nipples each. I guess you could still think of them like that. Her nip-nubs are just really flat or something.