THE SIGNIFICANCE OF THE CAUDAL EPIDERMIS IN ASCIDIAN METAMORPHOSIS

¹ Department of Zoology, University of Washington, Seattle 5, Washington

1. Tail resorption in Amaroucium is a rapid morphogenetic process. It is usually complete within only 6 minutes.

2. The initiation of tail resorption is signaled by a rapid separation of the epidermis of the tail from the underlying notochord-muscle-nerve cord complex (NMN-complex). This results in the formation of a fluid-filled subepidermal space. The NMN-complex buckles and folds as it moves into the posterior end of the trunk. The epidermis forms a thickened cap over the end of the trunk enclosing the other tail tissue.

3. When the tail was excised after the beginning of tail resorption, the epidermis was observed to retract independently of the other tail tissues.

4. The muscle cells do not manifest any tendency to shorten without the epidermis.

5. Potassium cyanide and sodium azide reversibly inhibit the onset of metamorphosis and slow down the rate of tail resorption if they are applied after the beginning of metamorphosis.

6. Some histological changes in the tail of Amaroucium and other species of ascidians may be the result of the activity of a proteolytic enzyme.