mic splitter

I am using macbooks in class and am looking for a cheap but effective device(splitter???) to allow two students to plug in two headsets(microphone and earphones) to work on a project.

Any suggestions would be appreciated.

Perhaps this is what your looking for

15cm (6") stereo headphone Y-adapter | Headphone Accessories | TheSource.ca

Those are headphone adapters - As you know you cannot plug a regular microphone into a mac built in jack...you either need USB or an adapter for the Mic. I found the Griffin adapeter for one mic I need one for two.