n GENERAL NATURE OF REGENERATION 593 



act of sexual reproduction in the ciliates (Calkins, 191 1 ; Moore, 1924). An act of regenera- 

 tion is not always completed during a single cycle of fission (Tartar 1941) so that it is not 

 "geared" completely to the mechanism which controls the latter. 



In the oligochaete, Dero (Berrill, 1952), removal of the tip of the tail, during architomy 

 (p. 588) in the middle of the body, does not inhibit fission, but it may inhibit subsequent 

 head-regeneration by the decaudated posterior daughter. By contrast, if the polychaete, 

 Procerastea, is transected in front of the fission plane at the time of incipient paratomy, a 

 head regenerates at the anterad cut surface even if it is within one body segment of the 

 developing head of the posterior daughter (Berrill, 1951, 1952). These facts are consistent 

 with rather precise chronological changes, during asexual reproduction and regeneration, 

 in the amounts of the same promotor and inhibitor substances (p. 636). 



Changes during a protozoon cycle of sexual reproduction are very different, if not com- 

 pletely inverse, and a commonly observed antagonism between regeneration and sexual 

 reproduction therefore may be due to metabolic incompatibility rather than to direct 

 competition between the two. However probably there is competition for materials in 

 some animals, e.g. in Hydra, for neoblasts (Brien, 1953); following transection of the body 

 regeneration may be slower on the side bearing an ovary than on the opposite side (Goetsch, 

 1929) while under other conditions transection leads to regeneration, but to resorption of 

 ovaries and testes (Goetsch, 1925). In Annelida, again, neoblasts probably are used for the 

 production of both germinal and somatic tissues, (Korschelt, 1927 ; p. 199) ; a regenerate may 

 even draw off" cells from the gonad itself {ibid. p. 202). Similarly the testes and yolk glands 

 of planarians are resorbed as material for regeneration (Steinmann, 1908). Such competi- 

 tion is inevitable in animals habitually operating near the limits of their productive meta- 

 bolism. 



Further analysis is necessary to establish particular instances as competitive or 

 antagonistic interaction, for instance the retardation of sexual reproduction in the 

 rhabdocoele Stenostomian, by simultaneous regeneration-activity (Hartmann, 1922). 

 Some evidence does indicate an antagonism between the Vwo processes. The 

 sexual individuals or gonozooids of the coelenterate Hydractinia regenerate very 

 poorly compared with the vegetative hydrozooids (Hyman, 1940; p. 491) and 

 earthworms regenerate badly from cut surfaces in the genital region. The gonad 

 itself regenerates poorly in Annelida and Arthropoda (Korschelt, 1927, p. 659, 

 660), though in fact animals as highly evolved as mice are able to regenerate an 

 ovary, from new tissue, after complete spaying (Davenport, 1925). It would be 

 valuable to know if there is an R-phase at any stage of the growth, maturation 

 and development of the gametes and zygote of animals. The latter often has con- 

 siderable powers of regeneration, in early stages by a morphallactic reorganisation 

 called "regulation" (Huxley and De Beer, 1934), and later by "postgeneration" 

 (Morgan, 1901; Miinch, 1937), at first sight an epimorphic process, but in the 

 light of recent work (Townes and Holtfreter, 1955; Feldman, 1955) possibly a 

 reconstittition process, that is a redistribution of cells rather than a proliferation. 

 There follows a stage, which probably corresponds to the inflexible "mosaic" 

 stage of the ontogenic processes themselves, during which regeneration does not 

 occur readily (Harrison, 191 5; Lehmann, 1929; Holtfreter, 1938; Murtasi, 1938; 

 Murtasi and Sosnina, 1943). This stage may also correspond to the stage during 

 regeneration when re-regeneration cannot be induced (Davidson and Berrill, 

 1948). After the mosaic stage, embryos enter the definitive stage, of recovered 

 regenerative power. The necessary local dedifferentiation and return to an em- 

 bryonic condition again becomes possible. In the higher animals the final age- 



Literature p. 64g 



