Janie, just drill a little hole and enjoy the latest fad- colored fingers!
My Canon cartridges look like they have in part a sponge-like filling. I have always suspected that only half the ink was delivered before they quit, and Gnu's first post adds a little weight to that.

A Google adv. below this post from Canon.ca/Ink states free same day shipping on $100+ orders. I think I am into the thousands by now. I think inks keep both Canon and Staples profitable.

There are cheaper substitutes, but people I know who have tried them have gummed up their printer.