Quarterly Journal of Microscopical Science, Vol s2-65, 643-697, Copyright © 1921 by Company of Biologists

Memoirs: Studies in Dedifferentiation

II. Dedifferentiation and resorption in Perophora

¹ Now College, Oxford

1. The social Ascidian Perophora viridis may dedifferentiate in either of two distinct ways, or by a mixed method : (a) by reduction to a spheroidal mass, as in Clavellina; (b) by incipient reduction as in (a), but followed by total resorption into the stolon, which may grow during the process.

2. Resorption is due to the migration of the individual cells out of the tissues into the haemocoel.

3. In certain conditions the zooid maintains itself, in spite of food not being provided, at its original size and in perfect health. This it does by resorbing the stolon.

4. Experiments with dilute solutions of KCN show that resorption of the zooid occurs in slightly unfavourable conditions, which affect the sensitive zooid. more than the less highly-organized stolon.

5. The results are to be explained as follows: (a) In the competition between zooid and stolon the zooid normally is dominant because metabolic processes take place at a greater rate in it than in the stolon. The stolon is therefore starved at the expense of the zooid. (b) The zooid is more susceptible than the stolon to toxic agencies, (c) In low concentrations of such agencies it is therefore affected while the stolon is not. (d) As a result it begins to dedifferentiate. Dedifferentiation is here accompanied by the migration of the cells out of the tissues, (e) The speed of its metabolic processes is now no longer greater than that of the stolon's. It is therefore now starved at the expense of the stolon. (f) Any cells migrating out of the tissues are removed by the normal circulation, by the stolon-circulation (irregular pulsation of the stolon), or by utilization as food by the stolon. As in chemical reactions where the end-products are removed, the reaction thus runs to its limit, i.e. to complete resorption of the zooid.

6. Stopping the circulation by means of KCl results in dedifferentiation accompanied by a much smaller degree of resorption.

7. At low temperatures (about 5°C.) some dedifferentiation occurs; but there is very little resorption, apparently owing to the cessation or slowing of the heart-beat.

8. Partial dedifferentiation is recorded in Amaroucium and Botryllus.

9. The significance for general biological problems of dominance due to high rate of metabolism, of differential susceptibility and of dedifferentiation, is discussed.

10. The similarity of certain psychological and neurological phenomena is noted (mental regression, alteration of spinal reflexes when freed from cerebral control, &c).