A humanoid species whose children can breathe only methyl oxide until about the age of four, seen on Rigel X in 2151 when Trip Tucker misread a mother weaning her child.
The Lorillians are a humanoid species known for an unusual feature of their development. Their infants cannot breathe oxygen and depend on methyl oxide for roughly the first four years of life, after which the mother gradually weans the child onto an oxygen atmosphere.
They appear in the Enterprise pilot, Broken Bow. While searching the trade complex on Rigel X in April 2151, Commander Tucker sees a Lorillian woman holding a gasping child away from a breathing device and assumes she is harming it. T'Pol stops him from stepping in and explains what the mother is doing.
The scene is an early lesson for the crew of Enterprise NX-01 about judging alien customs by human standards, and it sets up the friction between Tucker and T'Pol that runs through the first season.