6o8 REGENERATION AND GROWTH 7 



scanty. Moore (1910) found that a sigmoid curve related it to temperature, but 

 Florence Moog (1942) obtained a linear relation, in the same animal, Tubularia, 

 though the size of the hydranth-primordium declined with temperature along a 

 sigmoid curve. The rate/temperature relation described by her probably would be 

 sigmoid over a wider temperature-range. The action of most other variables at 

 present must be considered qualitatively only. 



A word seems necessary on the measurement of regeneration-rate in Arthropoda since 

 (a) the group is of critical value for accurate measurements and (b) the complication of 

 ecdysis leads to conceptual difficulties. Although occasionally an individual is "caught" 

 releasing an incompletely differentiated regenerate at ecdysis (O'Farrell and Stock, 1953, 

 1954) usually eclosion is all-or-none and, up to a critical stage, ecdysis is delayed until an 

 "all" eclosion is possible. This led Paulain (1938) and others to regard the stadium or 

 intermoult as the true unit of time, rather than the clock and the calendar. In consequence 

 he found that virtually no experimental factor significantly affected "regeneration rate" 

 defined as the eclosion-size, though conceivably the intermoult may have been considerably 

 prolonged or shortened by retardations and accelerations of the true rate of regeneration. 

 The normal amount regenerated per day is relatively constant over a large range of body- 

 size (Needham, 1949a) but on the other hand is sensitive to deviations from normal con- 

 ditions. 



By contrast the amount regenerated in one stadium ("eclosion-size") although increasing 

 linearly with body-size (Needham, 1949a), is relatively insensitive to changes in conditions 

 because the duration of the stadium in fact is increased or decreased proportionately to 

 any retardation or acceleration of regeneration. The eclosion-length, therefore, is virtually 

 invariant under all conditions, at a particular age and it is this spatial measurement, and 

 not the time-measurement, which might be regarded as a fixed "unit" of regeneration. The 

 relative eclosion-length, per unit of body-size (Needham, 1949a), or as a fraction of the defin- 

 itive length of the regenerate (Charniaux Legrand, 1951), of course is invariant also in 

 age (body-size). Changes in phosphate-concentration and in pH affect eclosion-size very 

 little, but eclosion-time, and therefore the specific regeneration-rate, very considerably 

 (Needham, 1947b). 



Paulain went further and used as the measure of regeneration-rate the constant b of the 

 relation jv = iA:", where y is the eclosion-size, and .v is body-size, b therefore being invariant 

 not only under any variables affecting one stadium but probably also under those affecting 

 body-growth and regeneration throughout life. His wealth of valuable quantitative results 

 therefore have not yielded all possible information and it is unfortunate that more of the 

 original measurements are not available. The power relation, y = bx", is probably an unwar- 

 ranted complication here. The observed values of a were not very different from unity, indi- 

 cating that the linear relation, above, is adequate. 



V. METABOLIC CHANGES DURING REGENERATION 



In the R-phase (p. 595) there is locally an increase in acidity (Okunev, 1928, 

 1929), in electropositivity (Crane, 1950) and in reduction-potential (Okunev, 

 1932; Orechovitch, 1934). There is a decrease of oxygen uptake and increased 

 glycolysis, with the production of lactic acid (Okunev, 1933; Vladimirova, 1934). 

 Proteolytic activity increases, probably promoted by an increase in free SH-groups, 

 which are largely responsible for the increased reduction-potential (J. Needham, 

 1942). Later another reducing agent, vitamin C, also increases in amount (Ryv- 

 kina, 1940). Pentose nucleic acid-concentration decreases (Hyden and Rexed, 

 1944; Hyden 1947; NovikofT and Potter, 1948; Drochmans, 1950). The amount 



