How many catalytic converters does my 1998 Nissan Sentra GXE have?

I have had some exhaust issues, mainly rust causing part of the exhaust pipe to break free and fall off. The part that fell off is where I usually expect to find the cat, but I noticed there's a cat directly off the engine... and the thing connected to the pipe that fell off is a bit smaller. Is it another catalytic converter? Or ...what is it? This pipe is the piece connecting from about where the driver sits, to the muffler. thanx