Whats the inside of a stomach made of?

[WillNever]

Just ask any mathematician. Your body is a torus.

Mathematicians don't know gross anatomy, fraggle. There are ducts within the GI tract that open and lead from internal organs (such as the liver, gallbladder, and pancreas) that throw a wrench into your analogy.

As well, your GI tract is connected to your nasopharynx and eustachian tubes via your oral cavity. Too many openings for a donut.

 

[adoucette]

Are all animals toruses? We all eat, digest and excrete. Are there any animals that regurgitate excreta through their feeding aperture, so they don't actually have a doughnut hole? I don't know much about the lower phyla, but arthropods, mollusks and (as you note) worms share the chordate toroidal structure.

Yeah, the round worm figured out how to improve on the batch feeding process and thus the anus was formed allowing the digestive assembly line, but the poor flat worm had no such luck and thus only one opening. You can also see this in animals like jellyfish, coral, hydra, echinoderms etc.

 

[arfa brane]

Mathematicians don't know gross anatomy, fraggle. There are ducts within the GI tract that open and lead from internal organs (such as the liver, gallbladder, and pancreas) that throw a wrench into your analogy.

As well, your GI tract is connected to your nasopharynx and eustachian tubes via your oral cavity. Too many openings for a donut.

Meh, a mathematician would just say "ok, it's a punctured torus".

 

[Peter Kinnon]

Mathematics is a language designed to handle the very simple. Natural language, although still inadequate, is a much better tool to use for the enormous complexities of living systems.

 

[river-wind]

After egg fertilization in an animal the egg divides and creates a sphere of cells, know as the blastula. Depending on the species, gastrulation occurs in a few different ways, most importantly, creating a single dimple in the surface of the sphere which results in an internal sack, or a single dimple which then attaches on the far of side of the sphere where it creates a second opening, ending up as a donut of sorts. Cnidaria, Platyhelminthes, have only one opening and a gastro sack, while Potifera, Nematoda, Annelida, Arthropoda, Mollusca, and Chordata all have blastulas with two connected openings after gastrulation. In this secriond group, the fold-turned-tube will then develop into a complete gut with a connected mouth and anus.

from http://www.mun.ca/biology/scarr/Protostomes_vs_Deuterostomes.html

some photos of the gastrulation process: http://biology.kenyon.edu/courses/biol114/Chap14/Chapter_14.html

But yeah, once further development occurs, donut becomes a bit over-simplified. As noted, we end up with multiple holes, at least on the mouth end, and the GI tract/endoderm becomes much longer than the external epidermal tissue.