Hackworth had been in a few of these, normally in more industrial 
settings. The entrance was dug into the beach, but the rest of it was a 
floating tunnel, a tube full of air, moored to the bottom. It was a cheap way 
to make space; the Nipponese used these things as sleeping quarters for foreign 
guest workers. The walls were made of membranes that drew oxygen from the 
surrounding seawater and ejected carbon dioxide, so that seen from a fish's 
point of view, the tunnels
steamed like hot pasta on a cold steel plate as they excreted countless 
microbubbles of polluted CO 2 . These things extruded themselves into the 
water like the roots that grew out of improperly stored potatoes, forking from 
time to time, carrying their own Feeds forward so that they could be extended 
on command. They were empty and collapsed to begin with, and when they knew 
they were finished, they inflated themselves with scavenged oxygen and grew 
rigid.