Scully cyrochamber air tube

Scully in one of these blocks of ice. Note the breathing tube.

In the massive alien craft in Antarctica, there were cryogenically frozen lifeforms all over the place.  Within the blocks of ice were stored both Humans and aliens.  They seem to be mere blocks of ice held in place by metallic frameworks and the individuals inside kept alive by a breathing tube and possibly other intravenous feeds.  It is likely some machinery helps maintain the temperature. 

Alien Cyrochamber hallway more overgrown with ice

Hallway of cyrogenically stored beings. Overgrown with ice.

Agent Fox Mulder traveled around the ship in his search for Agent Dana Scully.  One of the earliest passages filled with frozen beings had become overgrown with ice.  The passage where he found Scully was newer and the ice had not grown beyond the blocks with
Alien Cyrochamber hallway less overgrown with ice

A new corridor of frozen subjects. Ice blocks have not overgrown from frames.

people in them.  This suggests how long some have been frozen and that once the blocks are placed, the ice is allowed to build beyond the original blocks and frames that contain each frozen individual. 

Mulder flashlight on occupied cyrochamber

Mulder's flashlight illuminates one of the countless cyrogenically frozen people.

It is unknown how many frozen people and aliens were in the ship.  Hundreds, perhaps thousands.  When the ship began its startup sequence, the ice began to thaw and a Long-clawed alien attacked Mulder and Scully as they escaped from the ship. 

("The X-Files: Fight the Future")