Final answer:
The tapetum lucidum is part of the choroid coat in the eye's vascular tunic, which aids in low-light vision in certain animals.
Step-by-step explanation:
The tapetum lucidum is part of the choroid coat, which belongs to the vascular tunic of the eye. Its reflective properties help animals see in low-light conditions. This structure is not present in human eyes, but it is a characteristic feature in the eyes of many animals, including cows. The question details the appearance of the tapetum lucidum when observed with the retina removed, noting it is blue, shiny, and reflects light. From the given choices, the correct answer that defines the layer containing the tapetum lucidum is the Choroid (Option D), as it is a highly vascularized layer of connective tissue providing a blood supply to the eyeball and contains the tapetum lucidum in certain animals.