It is interesting to see two such widely different organs developed from a common origin; and as the movable lip of the cell serves as a protection to the zooid, there is no difficulty in believing that all the gradations, by which the lip became converted first into the lower mandible of an avicularium, and then into an elongated bristle, likewise served as a protection in different ways and under different circumstances.
izan ere, avikularioz hornituriko espezie guztiak iraungi egin direla joz gero, inork, irudimenik bizienaz ere, ez zukeen sekula pentsatu bibrakuluak hasieran txoriaren mokoaren, edo kutxa irregular edo txano baten antzeko organo baten zati izanik existitu zirenik.