slugs spitting stuff???

[fresh]

Hey all

I just noticed last night that I have two brownish looking slugs that have a very small shell/hat on top of them that just were spitting some kind of eggs or sperm or something similar!!!

They were spitting it once every 3 seconds, and after a short while, the top of my tank was covered by a mat of that stuff!!!

Is this bad or good? What should I do? What the heck are these?

Let me know if you have any ideas.

Thanks
Fresh.