As the jock notices the seat next to him he instinctively takes a seat placing his ass over the dildo and going all the way to the seat.
This wasn't bad at first but as he sat there and the instructor used his wand to point out the particulars of this muggle he noticed a warming in his ass.
The dildo seemed to be vibrating and his cock seemed to be growing hard and dripping precum.
As he sat there it grew longer and longer till his cock was resting on the floor with a puddle growing there.
Grab your penis the instructor said.
Not wanting to disobey the instructor he did so even though he wanted to resist.
Put the end in your mouth and lick up that goo you are dripping.
As he did he noticed that his ass was growing tighter and tighter around the dildo.
As he sucked he noticed that it wasn't his ass growing tighter the dildo was growing in size stretching out his hold and his insides pushing his organs up inside of him. As he grew more and more horny he noticed that he abdomen became more and more stretched out causing his cock to grow longer to arc around the mound that was now his belly. It looked like he swallowed a medicine ball.
His balls grew to the size of basketballs and dropped to the floor.
Now students do you know what this young jock is being prepped for?
The vacant looks on their faces told the teacher they had no idea what he was doing.
He is needed for breeding magical beasts. We had to stretch out his ass to accommodate all sorts of creatures even to the size of a dragon or a hippogriff.
Then why give him such a large cock and balls.
His cock is made large so that he has a source of nourishment as he endures the hours and hours of sex he will be used for. His balls release markers letting the creatures know he is in heat. He will not be able to use his cock to breed with and his balls will no longer produce the muggle cum but since there will be no release for him his balls will grow larger and larger.
Now for his first creature.