II 



GENERAL NATURE OF REGENERATION 



591 



TABLE 1 



MINIMAL SIZE OF FRAGMENT CAPABLE OF REGENERATING A WHOLE ANIMAL 



Species and group 



Minimal size 



Percentage of 

 parent-body 



Reference 



Lillie, 1896; Weisz, 1954; 

 Morgan, 1901, p. 56 

 Brien, 1937 



Peebles, 1897; Koelitz, 191 1; 



Korschelt, 1927; p. 581 



Lillie, 1900 



Holmes, 191 1 (by repeated 



section) 



Coe, 1929 (by repeated 



section) 



C. Muller, 1908 



rians, for instance Procotyla, have very poor powers compared with typical species 

 (Brondsted, 1955) and there is a similar variety among rhabdocoele Turbellaria. 

 These variations have yet to be compared with differences in normal growth rate 

 and other relevant properties. The cestode and trematode Platyhelmia are said 

 to have low powers of regeneration (Korschelt, 1927) notwithstanding their 

 enormous powers of growth and of asexual reproduction. Other parasites also are 

 reported to regenerate poorly (Morgan, 1901, p. 146; Kocian, 1930; Reinhard, 

 1952). In fact, as for certain species of Protozoa (Weisz, 1954) results obtained so 

 far may show poor survival under experiment, rather than poor regeneration. 



(b) Regeneration and other growth processes 



Regeneration-rate, like normal growth-rate, declines with age (p. 607). Przi- 

 bram (191 7) found a correlation between the growth-rate of individual stick- 

 insects and the rate of regeneration of their limbs. Growth-rate and regeneration- 

 rate show the same seasonal fluctuations (Otto, 1921 ; Needham, 1949a). Annelids 

 regenerate best at cut surfaces near the hind end of the body where growth and 

 asexual reproductive processes occur most rapidly and Protozoa regenerate best 

 at surfaces near the normal fission-plane (Tartar, 1941). The gonadal hormones 

 (p. 632) promote the regeneration of those organs of which they promote the nor- 

 mal growth (Korschelt, 1927, p. 665). The gonopod of the fish Platypoecilus regener- 

 ates rapidly if amputated during its normal growth-phase, but slowly once it 

 has entered the phase of differentiation (Grobstein, 1947). It seems doubtful if 

 any agent affects regeneration in a way incompatible with its known effect on 

 normal growth. 



Since growth and regeneration are so similar, the two processes often compete, 

 particularly where materials, etc., are limiting. In Hydra (Tardent, 1954) a regen- 

 erate and a normal asexual bud compete for the neoblast, interstitial cells which 

 are raw materials for both. In the isopod Crustacean, Asellus, regeneration tends 



Literature p. 64g 



