Yes, as Chris says, they're like humans in that they only start off with so many eggs, and once they've all been laid, that's when they stop.
I also read something somewhere about the eggs being arranged in "strings" inside the ovary, so that when a string runs out, that's what triggers a moult, and the loading of a new string. That may be utter rubbish though (it certainly sounds a bit far fetched!). [member=23925]chrismahon[/member] , do you know if there's any truth to this?