[Radula replacement and cell proliferation in the X-irradiated radular gland of the slugLimax flavus L. On the function of the radular gland epithelia].

Investigations have been carried out on the long-term effect of a single whole body X-irradiation on radula, radula replacement rate, and radular gland ofLimax flavus L. 1. Damage in the radula. In the course of 8 weeks after irradiation with 50 000 R two separate damaged areas develop in the radula. Immediately after exposure 1-2 transverse rows of defect teeth arise. Posterior to an area with normal transverse rows an extensive zone of malformed teeth develops from the 2nd week on. Normal transverse rows are produced again after the 8th week. 2. Replacement rate. Adult snails replace 3-3,5 transverse rows/day during 5 weeks after a dose of 40250 R. The replacement rate decreases to 1,1 rows/day in the 6th week (Fig. 3, broken-lined graph). 3. Damage in the radular gland epithelia. After irradiation with 50 000 R the proliferation zones of thesuperior andinferior epithelium differ with respect to the extent of damage. In the first mentioned area numerous cells die; the cell proliferation is strongly reduced for weeks and reaches a normal level again at the beginning of the 10th week after exposure. The superior epithelium and its proliferation zone are temporary atrophied (Fig. 5a, b and 7a, b). They have recovered in the 10th week. The mitotic activity in theinferior epithelium is less reduced than in the proliferation zone of the superior epithelium. It has almost normalized in the 5th week after exposure. Only a few inferior epithelium cells die; atrophy of the inferior epithelium does not occur. From the 3rd week on after exposure the odontoblasts in numerous radular glands are deformed (Fig. 8). They assume their normal shape again in the beginning of the 10th week. No odontoblasts die after the irradiation. 4. CONTROLS: 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).