DEDIFFERENTIATION IN PEROPHORA 693 
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 dedif- 
ferentiation 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 domi- 
nance due to high rate of metabolism, of differential suscepti- 
bility 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.). 
LirERATURE List. 
Allen (1920).—‘ Science ’, 52, 1920, p, 274. 
Child, C. M, (1904).—‘ Arch. Ent, Mech.’, 17, 1904, p. 1. 
——- (1915 a).—‘ Senescence and Rejuvenescence’, Chicago, 1915, 
—— (1915 b).—‘ Individuality in Organisms ’, Chicago, 1915. 
—-— (1916).—* Journ. Morph.’, 27, 1916. 
—— (1917).—Ibid,, 30, 1917. 
