At first look, the titles for the new Pokémon, Pocket Monsters X and Pocket Monsters Y, sound like its creators are out of ideas. They sound like a joke—no wonder why they were perhaps suggested as such in 2008. But dig a little deeper (way deeper!), and things get interesting.
Xerneas and Yveltal look very organic.
Xerneas represents a Neuron, Yveltal represents Muscles and Blood.
That means 2 of the 3 germ layers are covered.
Almost all animals develop out of 3 layers.
The third missing layer is the Endoderm.
The third legendary will represent the Endoderm.
This is some seriously deep and geeky theorizing, which is nothing new to Pokémon games (remember that Ground Zero theory in Pokémon Black/White?). This latest theory also makes sense! Have a look at this image (click for full size):
Kotaku is following up with Nintendo and will update this post should the company comment.
Update: J.C. Smith, director of Consumer Marketing, The Pokémon Company International told Kotaku, "The theory is fascinating and well thought out! I'm just as curious to know as you are. The origin of the title names for Pokémon X and Pokémon Y is something GAME FREAK may answer down the road. I can say that the names help unify the experience internationally because they're the same worldwide, which is great considering Pokémon X and Pokémon Y will be the first Pokémon titles to launch simultaneously around the world."
All Higher Animals Developer Out of 3 Germ Layers [Turnip's Tumbles]