[Zope] How to limit the number of Zope processes?

I run Zope 2.4.3 on Linux-x86. I would like to limit the number of Zserver processes that are automatically started, in order to manage my server resources. I have found the -t option which limits the number of threads per process, but I couldn't locate any configuration for the number of processes. If this is not configurable, could someone point me to the location in the code that starts new processes? Thanks, Gregory Popovitch