Answer: Trichuris trichiura (whipworm), cross-sections
There was a lot of great discussion for this case. Multiple readers mentioned the characteristic eggs (described as "lemon", "tea tray" or "football" shaped) with bipolar plugs (arrows below) which are characteristic for T. trichiura. This is best seen by narrowing the condenser - something I teach to all of my students!
Note that some of the eggs resemble those of Enterobius vermicularis, and therefore you would need to consider that parasite in the differential and carefully examine the sections for bipolar plugs.
Arthur Morris also mentions that the low power magnification nicely demonstrates the thin anterior end as well as the thicker posterior end - another diagnostic feature for T. trichiura.
Finally, there is a clearly identifiable stichosome in the anterior portion of the worm - something that I should have highlighted in my initial images - which is also characteristic for T. trichiura and closely related worms (Trichinella, Capillaria).
"this is why we have to crack the 'whip' when teaching pathology! We can't just serve up all this knowledge on a 'tea tray' and expect them to get it. If one can focus on the case and not let the overwhelming pressure of the image 'prolapse' your brain, you'll eventually sort it out."
Or from Florida Fan "Most students need only to learn the simple truth: 'nothing ventured, nothing gained,' and they should love to 'whip' the 'worm' till the foot balls are out, avoiding a 'prolapse at the rear'."
And from Blaine:
This specimen is from the (rectum),
I think it nearly (killed him)
To rock (a worm), that'll make (you squirm)
It's Trichuris trichiura, here we go...
[RUN-DMC fans will get the reference...}
Or for the Star Wars Fans:
Princess Leia was always proud of her Cinnabon hair
Until something similar poked out of her rear
With hyaline bipolar plugs,
This can only be one bug
It's Trichuris trichiura down in the derriere
You are all so creative - I love it.