Relations between the twisted bilateral structure of the cortex of the wool fiber and its ex ternal shape are pointed out. Both the crimped form and the elliptical cross-sectional shape follow the twisted internal structure. Changes in crimp shape are interpreted as a consequence of the unequal expansion of the ortho- and the paracortex. The geometrical relations of the crimp and ortho- and paracortex are traced back to events occurring during keratinization of the fiber.
