Spiders do not have a skeleton inside their bodies. They have a hard outer shell called an exoskeleton . Because it is hard, it can t grow with the spider. That means young spiders need to moult or shed their exoskeleton. The spider must climb out of the old shell through the cephalothorax. Once they are out they must stretch themselves out before the new exoskeleton hardens. This gives them a bit of growing room. As adults, they stop growing and do not need to moult.

I shouldn t have tried to grab my book. It was sliding across the floor towards the stairwell and as I was about to grab it, it slid under the railing. I looked around the hallway. There was no one around. No one was on the ground floor either, as far as I could see and the bell for the second period was about to ring. I jump down but misjudge the landing and land on my wrist. There s a slight crack. Before I can think about anything like if it s broken or not, MJ and Ned look down from above at me.
Peter? I look up, cradling my arm.
Hi. Did you fall? Just a little bit. They run down the stairs and meet me at the bottom step where I landed. MJ has a quick look and pokes at it gently. I flinch away Yeah, I think it might be broken. Oh crap.
We should...go to the sick bay. Ned suggests.

On our way there though, we bump into the deputy principal as the bell rings. What are you doing out of class? She asks.
We think Peter broke his arm. She takes in the scene of me cradling my arm.
Right. Take him to the sick bay and call your guardian. They can take you to the emergency room. We nod, and with my good hand, I take my phone out of my pocket. Thankfully, it s not smashed. Hey, Aunt May? Could you come and pick me up? There s a silence for a moment where I can hear her breathing.
I m on my way.

We wait on the front steps after the nurse has okayed me to go home. She pulls up in her battered car.
What did you do this time? I, uh, fell down the stairs. She shakes her head.
Only you. Get in.

We drive to the after hours in relative silence. Once we re in there, we have to wait for half an hour before we get to a triage nurse to see if it s broken or not. Finally, we get to the x-ray room where a guy explains what will happen. I ve had an x-ray before, when I was six and broke my collarbone, again, falling down some stairs. I put my wrist on the table while he adjusts the machine and puts a little card saying which arm it is beside it. He and Aunt May go behind a screen and he turns the machine on. After the x-ray s done, and it s up on the computer screen, he looks at it in confusion. He and Aunt May come through to where I am. I m not sure what s happened, but it looks like you don t have bones. My eyes widen. This isn t a Spiderman thing, is it? I think you might have moved a bit and blurred the picture, so we ll do it again, okay? I nod. They go back into the little room and do the procedure again. The doctor shows us the second results.
If I didn t know better, I would say that you ve got some sort of mutated exoskeleton instead of normal human bones Can I make a call? I say after he shows me the second x-ray pictures.
Sure, but come back in here when you ve finished. The doctor says. I dial Tony s number.
Mr Stark? Did you know spiders don t have bones? I ask, recalling something I learnt in biology. He doesn t answer for a moment.
What? He sounds confused, What did you do kid? I, uh, fell down some stairs and I think I broke or fractured or something, either way, I landed on my wrist and, uh, had an x-ray. My bones aren t showing up on their machine, just an exoskeleton kinda thing, I dunno what it is. I mean, I know I ve got the super-fast healing thing and all that but the photos and stuff are on their computer. There s another pause.
Where are you? I m on my way.