We have no more reason to believe in such a relation than we have to believe that the similar bones in the hand of a man, wing of a bat, and fin of a porpoise, are related to similar conditions of life.
No one supposes that the stripes on the whelp of a lion, or the spots on the young blackbird, are of any use to these animals.
The case, however, is different when an animal, during any part of its embryonic career, is active, and has to provide for itself.
The period of activity may come on earlier or later in life; but whenever it comes on, the adaptation of the larva to its conditions of life is just as perfect and as beautiful as in the adult animal.