Teratoma

Mature cystic teratoma

An ovary (more specifically, an ovum) trying to make a (?haploid) human on its own (without a spermatocyte). And gets quite far in the process.

Bronchial epithelium, cartilage, mucosal glands (lungs)

Bronchi, cartilage, mucinous glands

Bronchial mucosa, cartilage and glands (lungs)

Mucinous columnar epithelium (? lungs)

Normal ovarian corpus luteum and stroma

Squamoid fragments (? mouth, maybe tooth)

Thyroid ('struma ovarii') , surrounding a cartilage

Neurons with synapses

Neurons

Thyroid

Thyroid with columnar epithelial lining

Eosinophilic endocrine glands (? adrenal)

Intestinal looking glands

Deep staining endocrine glands

Haploid organisms are quite common through evolution; https://www.cell.com/developmental-cell/pdf/S1534-5807(17)30345-3.pdf 

A worm inside the appendix

Enterobius vermicularis on cross section of an appendix (9 year old child), replete with eggs.

Two worms (or a single worm in two planes) inside the lumen; note the vegetable matter inside

Inside of the worm

Characteristic Enterobius eggs

Recognition of tissue from histological sections with machine learning

A fresher in pathology. Only it's not a human, but a machine.

https://tissue-classifier.onrender.com

Thanks Sayak Paul.

Simulation of biological neurons

Can neurons (and neural pheonomena) be reverse engineered? Brian2 allows making customised 'neuron' objects with voltages, refractory period and synaptic delay etc. Here is a thought experiment on how far things can be stretched!
https://github.com/cmacus/biological_neuron_simulator