76 Regulation of Size in Unicellular Organisms 



shown later, how reproduction is related to the size of 

 the adults when ready to reproduce. 



Inheritance. That rate of reproduction is inherited 

 within each species might almost be assumed. That it 

 is inherited within, and differs in value for, each of 

 many races of one species, has been repeatedly demon- 

 strated upon infusoria under controlled cultural con- 

 ditions 11 . 



Under apparently identical conditions it is possible 

 to select from a single clone fast-fissioning and slow- 

 fissioning lines (Middleton, '15; Parker, '27). It may 

 be that these differences are due to unequal distribu- 

 tion of bodily material (Petersen, '27) or of genes (De- 

 Garis, '28) to the offspring, or that the diversities arise 

 during "reorganization" processes of some sort. 



Depressions. Over long periods of time, marked de- 

 creases in the rates of vegetative reproduction have 

 often been observed. Whether these are due to exter- 

 nal or to internal contingencies has been one of the 

 the major problems of protozoology. Permanently 

 downward trends in the rates of reproduction have 

 been regarded as deteriorations of the internal capa- 

 bilities of propagation. In every case investigated, 

 however, some influences of environmental factors up- 

 on the rates of deterioration have been found 12 , and in 

 many cases the running down has been shown to be 

 unnecessary and controllable 13 . 



Reorganizations. Not only long-continued down- 

 ward trends but also cyclic trends or rhythms in rates 

 of reproduction have been observed. These w T ere cor- 



n Jennings and Lashley (*13a), Jollos ('21), Middleton (*15), Parker 

 ('27). 



"Woodruff ('08), Baitsell ('14), Jennings ('20), Beers ('26, '28a, '28b), 

 Austin ('27). 



"Woodruff ('lib, '21, '25, '29), Enriques ('16a), Hartmann ('17), Mast 

 ('17), Metalnikow ('22), Chatton and Chatton ('23), Belar ('24), Spencer 

 ('24), Dawson ('28), Woodruff ('28). 



