The spreading of mammalian utricular epithelia gradually decreases with the age of the animal from which the tissue was harvested throughout the culture period, while the spreading of avian utricular epithelia occurs extensively and independently of the animal's age. A) Outlines of representative images of mammalian utricular sensory epithelia derived from embryonic day 18, postnatal day 1 (P1) and P15 mice at 1, 24, 48 and 72 hr in culture illustrate the gradual reduction in tissue spreading with age (Davies et. al, 2007). B) Outlines of representative images of avian utricular sensory epithelia derived from P0, P60 and P180 chickens at 1, 24, 48 and 72 hr in culture illustrate the age-independent extensive tissue spreading. Scale bar, 1 mm.