During parasite research, everytime the seed-like desription is made, it's said that this is a tapeworm. I've found a picture (sorry that this is from an animal website....). As the article says; a Tapeworm is originally a long parasite "with a small head at one end and many tiny brick-like repeating segments making up the rest of the worm. It is the last segments of the chain that are released from the worm". This is what we see in stools.