The nictitating membrane found between the eyelid and the eyeball.
Option A
Step-by-step explanation:
Nictitating membrane is the structure which function as an eyelid and therefore is also known as third eyelid. It is completely formed in some animals like amphibians, reptiles, fishes, birds and mammals and some primates like lemurs, while it is present as a rudimentary tissue at the inner corner of eye in primates like chimpanzee, orang-utan and human etc. It is translucent in colour and helps in clearing and protecting the eye.