Rhonda wrote:

If the worm was longish and thin, it sounds like a roundworm.

The worm looked like this:

http://www.dogbreedinfo.com/images14...rmImg_1395.jpg

but I didn't think it was as white in color as in that picture. It
was mostly flat, and segmented, and tapered at one end.

Roundworms (if I'm not mistaken) are round (not flat) and smooth.

I've read on websites, a roundworm infestation can get so bad
that the worms are also in the stomach.

Well, I think this was a tapeworm. Do roundworms shed
rice-grain-sized segments out the annus? Remember, I did see 4 or 5
such dried segments in his bedding.