There are a few options depending what you plan on doing inside the liver.
Are you creating a lid that opens and closes or are you fading some of it away(and back). Are you creating a window to look into it…and so on.
Simply put yea select polys, points or edges and press backspace. If you Dont do it in point mode be sure to run an OPTIMIZE command while in point mode after to get rid of all the extra points.
I generally select all my points, make a duplicate of the object (hide it) and delete the points then I invert the selection on the other object (minus 1 row) and delete that way you have the lid and the box…or what ever.
You could do this with a boole…but that always turns into a pain later.
You could animate the alpha in the material.
or or or…
/randy