In many aquatic larvae we find that all the spiracles are closed up, or become functionless, except a pair at the hinder end which are associated with some arrangement - such as the valvular flaps of the gnat larva or the telescopic " tail " of the drone-fly larva - for piercing the surface film and drawing periodical supplies of atmospheric air.
Neither male nor female has wings; the rostrum is replaced by a functionless tubercle; and there is no alimentary canal.
He has observed that in young specimens of Siren lacertina (the larva is still unknown) the gills are rudimentary and functionless, and that it is only in large adult specimens that they are fully developed in structure and function; he therefore concludes that the sirens are the descendants of a terrestrial type of batrachians, which passed through a metamorphosis like the other members of their class, but that more recently they have adopted a permanently aquatic life, and have resumed their branchiae by reversion.
They hay e large heads, projecting incisors, no ears, almost functionless eyes and moderately long tails; the skin, with the exception of a few hairs on the body and frinr-es on the feet, being naked.
394), being apparently led to that conclusion through its functionless wings and the backward situation of its legs.
How would you define functionless? Add your definition here.