(a) Photomicrographs showing the penetration of the primary ducts (asterisk) to the urethral muscle (Um) during spring and high magnification of the marked area and (b) the change of the lining epithelium from bilayered epithelium (arrowhead) to stratified cuboidal (arrow) as that of the urethral epithelium (Ue). Secretory portions accompanied the duct (Sp), blood vessels (Bv). Haematoxylin and eosin stain. (a) . (b): .