Head-shielded snails were irradiation with 50 000 R for controls. No effects of the body irradiation were found in the radula or in the radular gland epithelia. 5. Division of labour in the radular gland. The temporary elimination of the superior epithelium and the epithelial region above the odontoblasts-groups does not affect the tooth-formation and the radula transport into the oral cavity. Hence it follows: a) The odontoblasts-group is exclusively responsible for the definitive shape of the tooth (Fig. 8 and 9). b) The radula is transported into the oral cavity by the inferior epithelium (cf. Chap. E, II, b). On account of these results it is possible for the first time to described comprehensively the division of labour in the radular gland (cf. Chap. E, V). 6. Development of abnormal radular gland epithelia. After irradiation with 50 000 R an abnormal epithelial system develops from the 2nd week on in the tip of the radular gland (Fig. 10a, b;aEep). It encloses sphaeric or tube-like cavities. In many cases they communicate with the lumen of the radular gland. The light-microscopic appearence of the cells of this abnormal epithelium resembles those at the tip of a non-irradiated radular gland (Fig. 11 a, b).