What did you have in the jar with them? I used to take the whole leaf or branch on which an egg was laid, but lost eggs to (I think) tiny little spiders, earwigs and other hitchhikers that came along with the leaves. Now if I find an egg, I just snip a triangle out of the leaf with the egg, and I put that little piece on a damp paper towel and wait a few days until I see that there's a caterpillar there.
Sometimes I have seen a caterpillar turn right around and eat its own eggshell, but a lot of them don't. So make sure you don't have little caterpillars under the leaves!
Also, some of my eggs have turned out to be duds, they stay clear, never turn creamy-colored or dark where you can see the caterpillar inside. Guess those are infertile.