A well-developed tail having been formed in an aquatic animal, it might subsequently come to be worked in for all sorts of purposes, as a fly-flapper, an organ of prehension, or as an aid in turning, as in the case of the dog, though the aid in this latter respect must be slight, for the hare, with hardly any tail, can double still more quickly.
Uretako animalia batean buztan ongi garatua eratu zelarik, zernahitarako erabiltzeko eraldatu zitekeen gero, euli-uxagailutzat, oratzeko organotzat, edo biratzeko organotzat, txakurraren kasuan bezala, honen kasuan laguntza honek nahitaez txikia izan behar duen arren, izan ere, erbiak, buztanik ia ez duen arren, txakurrak baino askoz azkarrago egin baitezake bira.