i. Vestigial organs are those, which are present in reduced form in the organism and are functionless. Hence, their presence is not required.
ii. However, they continue to exist before they degenerate and disappear in the process of evolution.
iii. They were well developed and functional in the ancestors, but became reduced and functionless in the present day organisms due to change in habitat and habit.
iv. The study of vestigial organs suggests the process of evolution. It explains that present organisms have evolved from the ancestors, slowly, gradually and orderly.
v. In man, presence of the following organs indicates its use in the past:
a. Caecum and vermiform appendix: It is still seen in man as a functionless organ. It helps in cellulose digestion in herbivorous mammals.
b. Nictitating membrane: It is present in the eyes of humans and is a remnant of the third eyelid.
c. Coccyx or tail vertebrae: It is the remnant of a tail in human.
