What is this on the cylinder head next to spark plug? (pic)?

What is this on the cylinder head next to spark plug pic

The top is cracked off mine, honda nsr 80 and there's a connection that is supposed to go on top of it. Will my engine run without this connected?

"You can teach a man to fix a motorcycle, but if you teach him to find out how to fix a motorcycle he will know how to fix motorcycles forever." Jesus, First Corinthians. http://www.partsfish.com dude.