With slight information aside, the real reason for this section is for me to basically rant my opinions on Crona's gender. What's written here is my own theory and not accual facts.
My Opinion
Well let me start off by saying that I belive Crona to be a boy. Why you ask? I have seen various hints along the way that make me truely belive Crona is male. One of my thoughts could lead to why Medusa treats him so badly. She probaly had her mind set on a girl and when she had a boy, was furious. She dressed him like a girl, in hopes to make her feel better, but could not ignore the fact that she had a son.
So to punish him, she replaced his blood with the black blood and used him basically. Again, all of this is in theory and not the truth.
Proof That I Found
Most of my proof comes from episode 31, where it made me firmly belive that Crona is male.
Street Clothes
The clothes Liz and Patti (maybe just Patti) picked out for Crona are typical male street clothes. I would think these two would dress Crona up more feminie if he were a girl. His unsure look could be from my theory about Medusa as seen above...or those sunglasses. We can tell they did look for clothes because, by the looks of it it seems like Patti has the basketball unifrom in her hands that we see Crona in later on in the episode.
Formal Outfit
As seen here, all the girls, includeing Liz, are dressed in rather nice dresses. Crona, however, is dressed like the other boys, wearing slacks and a shirt. Now the top does look like what he wears underneith the black dress. This does not debunk why the wearing of pants. We know he does not wear them under the dress as well. So he had to have gotten the bottoms somewhere (clothes shopping with the Tompson Sisters), and they just happen to be pants and not something like what the girls are wearing.
You might say, "Well maybe Crona is tired of always wearing a dress, this prooves nothing." Ahh, but if I were a girl, having to wear a black dress all the time, I would want to look pretty at my own welcoming party, would'nt you?