Answer:
Those parts have become vestigial
Step-by-step explanation:
Organisms have a few parts that are not useful to them because those parts in them have become vestigial.
When an organism has a part that is no more used, it relates to the evolutionary history of such organism.
These parts are called vestigial body parts.
They are not needed for the survival of an organism again and they can do without them.
At a certain point in time, those parts might be very vital to the sustenance of such organisms.
With time, those parts become useless and redundant.