92 Regulation of Size in Unicellular Organisms 



2. Regeneration and Reproduction 



Regeneration, as a type of growth in size, has been 

 studied in relation to reproduction in a number of pro- 

 tozoan species. The invariable result was that repro- 

 duction failed to occur so soon in mutilated individuals 

 as in uncut individuals. But in how far this is due to 

 injury as such, to the mechanical stimulation, and the 

 like, rather thari to the loss of body substance itself, 

 is uncertain. 



Rate of regeneration of bulk. Measurements of the 

 rates at which the volumes of individuals are restored 

 after part of the body has been cut away are very few. 

 Sokoloff ('24) attempted some in Spirostomum and in 

 Dileptus ; he found that eventually adult size was com- 

 pletely regained, and that it took longer to regain this 

 size, the smaller the piece which was regenerating. 

 The rate at which body volume was regained cannot 

 be compared with the usual rate at which the volume 

 was increased by growth, because no data on the nor- 

 mal growth of individuals were obtained for either of 

 these species. It is known that growth in volume is 

 not always proportional to the mass which the individ- 

 ual already has at various times (Chapter 2). Whether 

 the rate of regeneration would correspond to the rate 

 of growth at each size, or at each age since cutting; or 

 whether the curve of regeneration differs essentially 

 from the curve of growth, has not yet been decided. 

 Data upon this point would serve to ascertain the rela- 

 tive importances of these two factors in increasing the 

 body size. 



At the present time it cannot be said whether re- 

 production by an individual cut to half its size will 

 occur earlier or later than that of an individual reduced 

 by normal fission to half its size. 



Will more total protoplasm result in cultures where 

 either reproduction or growth, or both, is hastened 



