ABSTRACT The dimensions of the semicircular canals of pike can be expressed as allometric functions of the body length L. The equal sensitivity of pike of different sizes to rotatory stimulation can be explained as a quadratic bending of the cupula. In the pike the sensitivity is of the same order of magnitude for the vertical and horizontal semicircular canals. In the pike the growth rate of the volumes of duct and ampulla is the same for the horizontal semicircular canal and for the posterior semicircular canal. The special growth rate of the dimensions of the horizontal semicircular canal of the ray can be explained by a quadratic bending of the cupula. For equally large cupulae the sensitivity of the horizontal semicircular canal is of the same order of magnitude for twenty-three mammals, fourteen birds and one reptile as it is for the pike. Within the limits of error the ‘growth rate’ of the diameter of the narrow duct is the same in mammals as in the pike. At the same body mass the absolute value of the diameter of the narrow duct is smaller in mammals than in the pike by a factor of 1·69. For a body mass of 1 kg the value of the enclosed area of the horizontal semicircular canal is 6 times smaller in mammals than in pike. The model of the overcritically damped oscillator for the semicircular canal remains valid during growth if a quadratic bending of the cupula is assumed.