592 REGENERATION AND GROWTH 7 



TABLE 2 



INHIBITORY INTERACTION BETWEEN REGENERATION 

 AND ASEXUAL REPRODUCTION 



(a) Regeneration inhibited by asexual reproduction 

 Example Reference 



Paramecium Tartar, 1941 



Planarians Vandel, 1922 



Dero, (Oligochaeta) Galloway, 1899 



(b) Asexual reproduction inhibited by regeneration 



Example Reference 



Amoeba Hartmann, 1924; Phelps, 1926 



Hydra Goetsch, 1921 



Stenostomum (Rhabdocoela) Hartmann, 1922 



Nais (Oligochaeta) Stolte, 1922 



Syllid Polychaetes Berrill, 1952; pp. 428-9. 



to inhibit growth competitively. In decapod Crustacea this inhibition is exercised 

 through the hormones of the eyestalk-organs (Kamps, 1937) known to control 

 growth and moulting more generally. 



The competition is not necessarily severe, when conditions are not limiting. 

 Tazelaar (1938) and Dixey (1938) detected no great effect of regenerating limbs 

 of arthropods on the growth of intact limbs and in fact competition may be masked 

 by a non-specific growth-stimulation by factors produced by the regenerate. 

 There may be, in consequence, a complex interplay of inhibition and acceleration 

 of normal growth (Przibram, 191 7; Huxley, 1932; Gabritchevsky, 1930) to which 

 other factors also contribute (p. 610). Accurate analysis demands a careful record 

 of growth- and regeneration-rates throughout. The phenomenon of '"relDound" 

 acceleration of normal growth after inhibition also may contribute to the com- 

 plexity; such rebound-effects have been recorded in regenerative growth also 

 (Morgulis, 1909; Du Noiiy, 1936, p. 92; Paton, 1955). 



In rhabdocoele and triclad Turbellaria, in microdrile Oligochaeta and probably also in 

 other groups, powers of regeneration are often closely correlated with powers of asexual 

 reproduction by fission, etc. (Berrill, 1951, 1952; Weisz, 1954). There is more evidence 

 (Table 2) of competition between the two processes than between either and ontogenetic 

 growth, because they are frequently evoked at the same time. Under different conditions 

 the one or the other may have the advantage in the same animal (Goetsch, 191 7, 1925; 

 Boecker, 192 1). In some Protozoa wounding may evoke either regeneration or fission, 

 depending on conditions (Summers, 1941). In Planarians also (Vandel, 1921) wounding 

 may accelerate fission. Regeneration is slow immediately after fission in Protozoa and 

 also after encystment (Calkins, 191 1; Moore, 1924) and improves progressively during a 

 subsequent "physiological restoration". The change is attributed to cyclic changes in 

 nucleo-cytoplasmic interaction during the cycle of fission (Bauer and Granowskaja, 1934) ; 

 it seems possible that a similar cyclic change may contribute to the observed depression of 

 regeneration-power during certain stages of a previous act of regeneration (Davidson and 

 Berrill, 1948). By contrast regeneration is said to be better just after, than just before, an 



